| Message ID | 1507613660-27236-1-git-send-email-john.stultz@linaro.org |
|---|---|
| Headers | show |
| Series | Overlay manager for predefined DT overlay fragments | expand |
On Mon, Oct 09, 2017 at 10:34:17PM -0700, John Stultz wrote: > In working with the HiKey and HiKey960 as targets for AOSP, > Dmitry developed the following overlay manager driver, which > allows a number of pre-determined DT overlay configurations to > be defined, and the configurations to be enabled at boot time > via a kernel boot argument. > > This has been submitted before, but while the earlier discussion > didn't really resolve to any sort of actionable direction, this > issue cropped up again and was a major discussion topic at the > Linux Plumbers Conference Android Microconference, so I suspect > it is worth revisiting this solution again. The Treble way to handle this is it is the bootloader's problem, right? > The overall use case is being able to configure devboards that > support a number of different mezzanine peripherals which > unfortunately cannot be probed. Some example mezzanines are > LCD panels or sensor hubs, as well as other options. There's probably some usecases for putting the overlay into the base DT, but I don't think mezzanine boards is one of them especially for dev boards where we may want to share overlays. I could see it in cases where you have 2nd source components for a product and want to select one. > The new functionality this driver provides is a mechanism to > specify multiple pre-determined dt overlay fragments in a > dtb file, and providing a way to select which dt fragments > should be applied via the kernel boot argument. > > The desire to use a kernel boot-argument as the selection > mechanism, comes from the Android Boot Image format not handling > dtbs independently. Usually with Android, the dtb is appended > to the kernel image, and modifying that is much more difficult > then changing the boot argugments. There is also a usability > argument that using a kernel command option to select > pre-defined entries is simpler for users to navigate. Doesn't Treble address the handling of overlays? Of course, none of what has been outlined for Treble has been reviewed upstream either... The concept seems fine, it's the vendor implementations that worry me. As far as usability, a RPi user would probably say listing overlays in a text file is easiest as that's how the RPi firmware works. > Also, since the mezzanines are unable to be probed, we cannot > use other solutions, like having the bootloader specify > additional dtb overlays to the kernel. Not sure I follow. Someone has to decide what to put on the kernel command line. If you are setting the overlay in the command line at bootimage build time or in the bootloader, then you could just apply the overlay at that point in time. Maybe it's slightly easier to change the kernel command line than change the dtb. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Oct 13, 2017 at 2:41 PM, Rob Herring <robh@kernel.org> wrote: > On Mon, Oct 09, 2017 at 10:34:17PM -0700, John Stultz wrote: >> In working with the HiKey and HiKey960 as targets for AOSP, >> Dmitry developed the following overlay manager driver, which >> allows a number of pre-determined DT overlay configurations to >> be defined, and the configurations to be enabled at boot time >> via a kernel boot argument. >> >> This has been submitted before, but while the earlier discussion >> didn't really resolve to any sort of actionable direction, this >> issue cropped up again and was a major discussion topic at the >> Linux Plumbers Conference Android Microconference, so I suspect >> it is worth revisiting this solution again. > > The Treble way to handle this is it is the bootloader's problem, right? I believe so, though with the treble approach, the device configuration is still somewhat fixed. Just that configuration is spread out between multiple partitions. Its a bit of a separate issue. >> The overall use case is being able to configure devboards that >> support a number of different mezzanine peripherals which >> unfortunately cannot be probed. Some example mezzanines are >> LCD panels or sensor hubs, as well as other options. > > There's probably some usecases for putting the overlay into the base > DT, but I don't think mezzanine boards is one of them especially for dev > boards where we may want to share overlays. > > I could see it in cases where you have 2nd source components for a > product and want to select one. > >> The new functionality this driver provides is a mechanism to >> specify multiple pre-determined dt overlay fragments in a >> dtb file, and providing a way to select which dt fragments >> should be applied via the kernel boot argument. >> >> The desire to use a kernel boot-argument as the selection >> mechanism, comes from the Android Boot Image format not handling >> dtbs independently. Usually with Android, the dtb is appended >> to the kernel image, and modifying that is much more difficult >> then changing the boot argugments. There is also a usability >> argument that using a kernel command option to select >> pre-defined entries is simpler for users to navigate. > > Doesn't Treble address the handling of overlays? Of course, none of what > has been outlined for Treble has been reviewed upstream either... The > concept seems fine, it's the vendor implementations that worry me. Again, I'm not sure how that connects to the proposal here. Having treble's multiple overlays being picked up in a standard fashion is nice, but how does that translate into a user booting a board with one mezzanine and then change the mezzanine and be able to get the new mezzanine to work with a minimal amount of fuss. > As far as usability, a RPi user would probably say listing > overlays in a text file is easiest as that's how the RPi firmware works. Right, and I agree that usability wise, its very similar to the cmdline arguments. But that requires firmware that keeps track of various overlays and has some small filesystem where that config file can be stored and easily updated. >> Also, since the mezzanines are unable to be probed, we cannot >> use other solutions, like having the bootloader specify >> additional dtb overlays to the kernel. > > Not sure I follow. > > Someone has to decide what to put on the kernel command line. If you are > setting the overlay in the command line at bootimage build time or in > the bootloader, then you could just apply the overlay at that point in > time. Maybe it's slightly easier to change the kernel command line than > change the dtb. Not, its not slightly easier, its much *much* easier to tweak the boot arguments. Since the dtb is appended to the kernel image w/ the abootimg format, its not simple at all to cut one out and replace it. While the cmdline is trivial to do with the abootimg command: abootimg -x boot.img vi bootimg.cfg abootimg -u boot.img -f ./bootimg.cfg and re-flash. This doesn't require access to the kernel source or rebuilding anything. It seems you're suggesting that there be some sort of special overlay partition which users have to flash with pre-built images containing the appropriate overlay dtbs, so that something like the treble overlay-per-partition approach could be used. And in the case with hikey/hikey960, this may be doable, as we can modify the UEFI source, but it would also require users to have all the various overlay images to flash as well, which adds complexity. Additionally on other boards which don't have open firmware, such a solution may not be feasible. The benefit to this approach is it doesn't require such standardized firmware behavior. I really do think there is value in the simplicity of this approach. thanks -john -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Oct 13, 2017 at 04:51:03PM -0700, John Stultz wrote: > On Fri, Oct 13, 2017 at 2:41 PM, Rob Herring <robh@kernel.org> wrote: > > On Mon, Oct 09, 2017 at 10:34:17PM -0700, John Stultz wrote: > >> In working with the HiKey and HiKey960 as targets for AOSP, > >> Dmitry developed the following overlay manager driver, which > >> allows a number of pre-determined DT overlay configurations to > >> be defined, and the configurations to be enabled at boot time > >> via a kernel boot argument. > >> > >> This has been submitted before, but while the earlier discussion > >> didn't really resolve to any sort of actionable direction, this > >> issue cropped up again and was a major discussion topic at the > >> Linux Plumbers Conference Android Microconference, so I suspect > >> it is worth revisiting this solution again. > > > > The Treble way to handle this is it is the bootloader's problem, right? > > I believe so, though with the treble approach, the device > configuration is still somewhat fixed. Just that configuration is > spread out between multiple partitions. Its a bit of a separate issue. > > >> The overall use case is being able to configure devboards that > >> support a number of different mezzanine peripherals which > >> unfortunately cannot be probed. Some example mezzanines are > >> LCD panels or sensor hubs, as well as other options. > > > > There's probably some usecases for putting the overlay into the base > > DT, but I don't think mezzanine boards is one of them especially for dev > > boards where we may want to share overlays. > > > > I could see it in cases where you have 2nd source components for a > > product and want to select one. > > > >> The new functionality this driver provides is a mechanism to > >> specify multiple pre-determined dt overlay fragments in a > >> dtb file, and providing a way to select which dt fragments > >> should be applied via the kernel boot argument. > >> > >> The desire to use a kernel boot-argument as the selection > >> mechanism, comes from the Android Boot Image format not handling > >> dtbs independently. Usually with Android, the dtb is appended > >> to the kernel image, and modifying that is much more difficult > >> then changing the boot argugments. There is also a usability > >> argument that using a kernel command option to select > >> pre-defined entries is simpler for users to navigate. > > > > Doesn't Treble address the handling of overlays? Of course, none of what > > has been outlined for Treble has been reviewed upstream either... The > > concept seems fine, it's the vendor implementations that worry me. > > Again, I'm not sure how that connects to the proposal here. Having > treble's multiple overlays being picked up in a standard fashion is > nice, but how does that translate into a user booting a board with one > mezzanine and then change the mezzanine and be able to get the new > mezzanine to work with a minimal amount of fuss. Perhaps I need to study how exactly treble systems will select all their overlays. Supporting different panels or other 2nd source components is a pretty common problem in production devices. Those aren't probe-able either and folks don't want to flash different images for each combination of h/w. > > As far as usability, a RPi user would probably say listing > > overlays in a text file is easiest as that's how the RPi firmware works. > > Right, and I agree that usability wise, its very similar to the > cmdline arguments. But that requires firmware that keeps track of > various overlays and has some small filesystem where that config file > can be stored and easily updated. > > >> Also, since the mezzanines are unable to be probed, we cannot > >> use other solutions, like having the bootloader specify > >> additional dtb overlays to the kernel. > > > > Not sure I follow. > > > > Someone has to decide what to put on the kernel command line. If you are > > setting the overlay in the command line at bootimage build time or in > > the bootloader, then you could just apply the overlay at that point in > > time. Maybe it's slightly easier to change the kernel command line than > > change the dtb. > > Not, its not slightly easier, its much *much* easier to tweak the boot > arguments. Since the dtb is appended to the kernel image w/ the > abootimg format, its not simple at all to cut one out and replace it. Appended dtb was to support legacy non-DT aware bootloaders. It never should have been carried over to arm64. > While the cmdline is trivial to do with the abootimg command: > abootimg -x boot.img > vi bootimg.cfg > abootimg -u boot.img -f ./bootimg.cfg It's easy because there is a tool to do so, not because a the kernel command line is inheritly easier to modify than a dtb. It would be trivial to write a tool or add to this one the code to find the dtb within the image and modify it. That's what every bootloader can do. Of course, abootimg is a horrible creation IMO. Why Android can't use something called a filesystem for the boot partition is beyond me. Then modifying it would not require special tools that could only modify whatever someone had the itch to modify. And combining the kernel, dtb, and overlays into a single file would not be necessary. > and re-flash. This doesn't require access to the kernel source or > rebuilding anything. > > It seems you're suggesting that there be some sort of special overlay > partition which users have to flash with pre-built images containing > the appropriate overlay dtbs, so that something like the treble > overlay-per-partition approach could be used. I'm not really suggesting anything. I'm not going to take something that *only* solves your usecase of apply an overlay embedded in a base dtb based on the kernel command line. I have no issue really with either one of those. What I don't want is another "overlay manager" for each usecase. And sorry, you don't win for being first (you're not really). All this I said before. > And in the case with hikey/hikey960, this may be doable, as we can > modify the UEFI source, but it would also require users to have all > the various overlay images to flash as well, which adds complexity. > Additionally on other boards which don't have open firmware, such a > solution may not be feasible. The benefit to this approach is it > doesn't require such standardized firmware behavior. Unless there's some great, overwhelming demand to support such devices with closed firmware, there's no benefit to me to care. What board do we have with closed firmware that needs this? Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Oct 17, 2017 at 12:46 PM, Rob Herring <robh@kernel.org> wrote: > On Fri, Oct 13, 2017 at 04:51:03PM -0700, John Stultz wrote: >> On Fri, Oct 13, 2017 at 2:41 PM, Rob Herring <robh@kernel.org> wrote: >> > Someone has to decide what to put on the kernel command line. If you are >> > setting the overlay in the command line at bootimage build time or in >> > the bootloader, then you could just apply the overlay at that point in >> > time. Maybe it's slightly easier to change the kernel command line than >> > change the dtb. >> >> Not, its not slightly easier, its much *much* easier to tweak the boot >> arguments. Since the dtb is appended to the kernel image w/ the >> abootimg format, its not simple at all to cut one out and replace it. > > Appended dtb was to support legacy non-DT aware bootloaders. It never > should have been carried over to arm64. > >> While the cmdline is trivial to do with the abootimg command: >> abootimg -x boot.img >> vi bootimg.cfg >> abootimg -u boot.img -f ./bootimg.cfg > > It's easy because there is a tool to do so, not because a the kernel > command line is inheritly easier to modify than a dtb. Maybe not in some theoretical sense, but practically it very much is easier. There are packaged tools available on most distros, user familiarity, etc. A bit of a tangent, but part of the reason why appended dtbs (despite being only for legacy platforms) are often used is because they make things simpler. At least for the boards I use, dtbs aren't static enough to be considered firmware. If I've got a new kernel to test, I usually have to copy a dtb over too. Managing separate files that are effectively tied together is a practical pain. With appended dtbs I never have to guess if some failure I'm seeing is because I forgot a step w/ the dtb. Now, maybe with boards like hikey and others getting upstreamed, there will be less dts churn there and I can happily forget to build and copy over new dtbs. But I'm not sure if that really is the common case yet. > It would be trivial to write a tool or add to this one the code to find > the dtb within the image and modify it. That's what every bootloader can > do. But would such a tool be usable? Or capable of being shared between boards? How does one enumerate or distribute fragments? These are all extra complexities with the pure dtb modification methods, which the embedded fragment + boot arg selection avoids. > Of course, abootimg is a horrible creation IMO. Why Android can't use > something called a filesystem for the boot partition is beyond me. Then > modifying it would not require special tools that could only modify > whatever someone had the itch to modify. And combining the kernel, dtb, > and overlays into a single file would not be necessary. While I agree the extensibility of abootimg (particularly in the dtb era) has been restrictive, I personally find it reasonably nice to work with. Being able to trivially modify the kernel and cmdlines w/o having to have root permissions to mount images is pretty nice. FAT filesystems can be similarly tweaked w/ mtools, but then you need a secondary bootloader, etc, and tweaking grub menus isn't as simple as the abootimg config file. >> and re-flash. This doesn't require access to the kernel source or >> rebuilding anything. >> >> It seems you're suggesting that there be some sort of special overlay >> partition which users have to flash with pre-built images containing >> the appropriate overlay dtbs, so that something like the treble >> overlay-per-partition approach could be used. > > I'm not really suggesting anything. I'm not going to take something that > *only* solves your usecase of apply an overlay embedded in a base dtb > based on the kernel command line. I have no issue really with either one > of those. What I don't want is another "overlay manager" for each > usecase. And sorry, you don't win for being first (you're not really). > All this I said before. So, I'm not actually asking anyone to take anything here, I'm just trying to reopen the conversation that hasn't gone very far, so we can find some direction to take. I've not followed the discussion super closely here, so apologies if I'm off base here. But it does seem there's a number of similar efforts, and it seems no one has gotten enough momentum to make a real push upstream. It seems its just easier for everyone to keep their own approach in their own tree and not to bother. At one end, sure, keeping half baked ideas out of mainline until they really sort themselves out is fine, but at the other extreme you risk the half-baked ideas calcifying in their own tree and then you have more Android (or whatever variant) specific cruft to shake your fist at. :) How do we get to a shared solution here where folks are engaging with upstream? Even an "I like approach B, go make that work" would help here. >> And in the case with hikey/hikey960, this may be doable, as we can >> modify the UEFI source, but it would also require users to have all >> the various overlay images to flash as well, which adds complexity. >> Additionally on other boards which don't have open firmware, such a >> solution may not be feasible. The benefit to this approach is it >> doesn't require such standardized firmware behavior. > > Unless there's some great, overwhelming demand to support such devices > with closed firmware, there's no benefit to me to care. What board do we > have with closed firmware that needs this? Just across the 96boards we don't have open firmware on all the boards. thanks -john -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Oct 17, 2017 at 2:20 PM, John Stultz <john.stultz@linaro.org> wrote: > On Tue, Oct 17, 2017 at 12:46 PM, Rob Herring <robh@kernel.org> wrote: >> On Fri, Oct 13, 2017 at 04:51:03PM -0700, John Stultz wrote: >>> It seems you're suggesting that there be some sort of special overlay >>> partition which users have to flash with pre-built images containing >>> the appropriate overlay dtbs, so that something like the treble >>> overlay-per-partition approach could be used. >> >> I'm not really suggesting anything. I'm not going to take something that >> *only* solves your usecase of apply an overlay embedded in a base dtb >> based on the kernel command line. I have no issue really with either one >> of those. What I don't want is another "overlay manager" for each >> usecase. And sorry, you don't win for being first (you're not really). >> All this I said before. > > So, I'm not actually asking anyone to take anything here, I'm just > trying to reopen the conversation that hasn't gone very far, so we can > find some direction to take. > > I've not followed the discussion super closely here, so apologies if > I'm off base here. But it does seem there's a number of similar > efforts, and it seems no one has gotten enough momentum to make a real > push upstream. It seems its just easier for everyone to keep their own > approach in their own tree and not to bother. At one end, sure, > keeping half baked ideas out of mainline until they really sort > themselves out is fine, but at the other extreme you risk the > half-baked ideas calcifying in their own tree and then you have more > Android (or whatever variant) specific cruft to shake your fist at. > :) > > How do we get to a shared solution here where folks are engaging with upstream? > > Even an "I like approach B, go make that work" would help here. Nudge. Any further thoughts on what sort of an approach might be viable here? thanks -john -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html