| Message ID | 20190108223953.9969-1-luca@lucaceresoli.net |
|---|---|
| Headers | show |
| Series | TI camera serdes - I2C address translation draft | expand |
Em Tue, 8 Jan 2019 23:39:49 +0100 Luca Ceresoli <luca@lucaceresoli.net> escreveu: > Hi, > > there has been some discussion on linux-media about video > serializer/deserializer chipsets with remote I2C capabilities from TI > [0] and Maxim [1]. I took part discussing how the remote I2C feature > of such chips could be best implemented in Linux while I was > implementing a driver for the Texas Instruments DS90UB954-Q1 video > deserializer. My approach is different from both the one used by > Vladimir Zapolskiy on other TI chips, which look similar to the > DS90UB954 in their I2C management, and the one used by Kieran Bingham > with Maxim chips, which have a different and simpler I2C management. > > After that I had to stop that work, so it is unfinished and I have no > plan to continue it. Upon suggestion by some linux-media developers > I'm sending my patches as RFC in the hope that they bring additional > material for the discussion. > > I2C management is quite complete in my patches, and it shows how I > envisioned I2C management. For the rest the code is in large part > incomplete. Don't consider the V4L2, GPIO and other sections as ready > for any review. > > The whole idea is structured around a central node, called the ATR > (Address Translator). It is similar to an I2C mux except it changes > the I2C addresses of transactions with an "alias" address for each > remote chip. Patch 2 has a detailed description of this process. > > > A typical setup looks like: > > Slave X @ 0x10 > .-----. | > .-----. | |---+---- B > | CPU |--A--| ATR | > `-----' | |---+---- C > `-----' | > Slave Y @ 0x10 > > A = "local" bus > B = "remote" bus 0 > C = "remote" bus 1 > > In patch 2 I enriched the i2c-mux to also act as an ATR. However the > implementation grew larger than I desired, so now I think it would > make sense to leave i2c-mux as is, and add a new i2c-atr.c which has > ATR features without much of the MUX code. However the implementation > would not change too much, so you can look at i2c-mux to see how I > implemented the ATR. > > In the ATR (i2c-mux.c) I implemented the logic needed to remap slave > addresses according to a table. Choosing appropriate aliases and > filling that table is driver-specific, so in this case it is done by > ds90ub954.c. The ATR driver needs to know when a new client appears on > the remote bus to setup translation and when it gets disconnected to > undo it. So I added a callback pair, attach_client and detach_client, > from i2c-core to i2c-mux and from there to the ATR driver. When > getting the callback the ATR driver chooses an alias to be used on the > local bus for the new chip, configures the ATR (perhaps setting some > registers) returns the alias back to the ATR which sill add the new > chip-alias pair to its table. The ATR (i2c-mux) then will do the > translation for each message, so that the alias will be used on the > local bus and the physical chip address on the remote bus. > > The alias address for a new client is chosen from an alias pool that > must be defined in device tree. It is the responsibility of the DT > writer to fill the pool with addresses that are otherwise unused on > the local bus. The pool could not be filled automatically because > there might be conflicting chips on the local bus that are unknown to > the software, or that are just connected later. > > The alias pool and the mapping done at runtime allow to model > different camera modules [or display or other modules] similarly to > beaglebone capes or rpi hats, up to a model where: > > 1. there can be different camera modules being designed over time > 2. there can be different base boards being designed over time > 3. there is a standard interconnection between them (mechanical, > electrical, communication bus) > 4. camera modules and base boards are designed and sold independently > (thanks to point 3) > > The implementation is split in the following patches: > * Patch 1 adds the attach_client() and detach_client() callbacks to > i2c-core > * Patch 2 adds similar callbacks for the use of device drivers and, > most importantly, implements the ATR engine > * Patch 3 adds a farily complete DT bindings document, including the > alias map > * Patch 4 adds the DS90UB954-Q1 dual deserializer driver > > There is no serializer driver here. The one I have is just a skeleton > setting a few registers, just enough to work on the deserializer > driver. Not sure what to do here... I guess I'll just mark the patches as RFC at media patchwork, as someone has to need support for it and need to finish its implementation. > > Each patch has an comprehensive list of open issues. > > [0] https://www.spinics.net/lists/linux-gpio/msg33291.html > [1] https://www.spinics.net/lists/linux-media/msg142367.html > > Regards, > -- > Luca > > > Luca Ceresoli (4): > i2c: core: let adapters be notified of client attach/detach > i2c: mux: notify client attach/detach, add ATR > media: dt-bindings: add DS90UB954-Q1 video deserializer > media: ds90ub954: new driver for TI DS90UB954-Q1 video deserializer > > .../bindings/media/ti,ds90ub954-q1.txt | 151 ++ > drivers/i2c/i2c-core-base.c | 16 + > drivers/i2c/i2c-mux.c | 218 ++- > drivers/i2c/muxes/i2c-mux-pca954x.c | 2 +- > drivers/media/Kconfig | 1 + > drivers/media/Makefile | 2 +- > drivers/media/serdes/Kconfig | 13 + > drivers/media/serdes/Makefile | 1 + > drivers/media/serdes/ds90ub954.c | 1335 +++++++++++++++++ > include/linux/i2c-mux.h | 20 +- > include/linux/i2c.h | 9 + > 11 files changed, 1760 insertions(+), 8 deletions(-) > create mode 100644 Documentation/devicetree/bindings/media/ti,ds90ub954-q1.txt > create mode 100644 drivers/media/serdes/Kconfig > create mode 100644 drivers/media/serdes/Makefile > create mode 100644 drivers/media/serdes/ds90ub954.c > Thanks, Mauro
Hi, On 21/05/19 19:40, Mauro Carvalho Chehab wrote: > Em Tue, 8 Jan 2019 23:39:49 +0100 > Luca Ceresoli <luca@lucaceresoli.net> escreveu: > >> Hi, >> >> there has been some discussion on linux-media about video >> serializer/deserializer chipsets with remote I2C capabilities from TI >> [0] and Maxim [1]. I took part discussing how the remote I2C feature >> of such chips could be best implemented in Linux while I was >> implementing a driver for the Texas Instruments DS90UB954-Q1 video >> deserializer. My approach is different from both the one used by >> Vladimir Zapolskiy on other TI chips, which look similar to the >> DS90UB954 in their I2C management, and the one used by Kieran Bingham >> with Maxim chips, which have a different and simpler I2C management. >> >> After that I had to stop that work, so it is unfinished and I have no >> plan to continue it. Upon suggestion by some linux-media developers >> I'm sending my patches as RFC in the hope that they bring additional >> material for the discussion. >> >> I2C management is quite complete in my patches, and it shows how I >> envisioned I2C management. For the rest the code is in large part >> incomplete. Don't consider the V4L2, GPIO and other sections as ready >> for any review. >> >> The whole idea is structured around a central node, called the ATR >> (Address Translator). It is similar to an I2C mux except it changes >> the I2C addresses of transactions with an "alias" address for each >> remote chip. Patch 2 has a detailed description of this process. >> >> >> A typical setup looks like: >> >> Slave X @ 0x10 >> .-----. | >> .-----. | |---+---- B >> | CPU |--A--| ATR | >> `-----' | |---+---- C >> `-----' | >> Slave Y @ 0x10 >> >> A = "local" bus >> B = "remote" bus 0 >> C = "remote" bus 1 >> >> In patch 2 I enriched the i2c-mux to also act as an ATR. However the >> implementation grew larger than I desired, so now I think it would >> make sense to leave i2c-mux as is, and add a new i2c-atr.c which has >> ATR features without much of the MUX code. However the implementation >> would not change too much, so you can look at i2c-mux to see how I >> implemented the ATR. >> >> In the ATR (i2c-mux.c) I implemented the logic needed to remap slave >> addresses according to a table. Choosing appropriate aliases and >> filling that table is driver-specific, so in this case it is done by >> ds90ub954.c. The ATR driver needs to know when a new client appears on >> the remote bus to setup translation and when it gets disconnected to >> undo it. So I added a callback pair, attach_client and detach_client, >> from i2c-core to i2c-mux and from there to the ATR driver. When >> getting the callback the ATR driver chooses an alias to be used on the >> local bus for the new chip, configures the ATR (perhaps setting some >> registers) returns the alias back to the ATR which sill add the new >> chip-alias pair to its table. The ATR (i2c-mux) then will do the >> translation for each message, so that the alias will be used on the >> local bus and the physical chip address on the remote bus. >> >> The alias address for a new client is chosen from an alias pool that >> must be defined in device tree. It is the responsibility of the DT >> writer to fill the pool with addresses that are otherwise unused on >> the local bus. The pool could not be filled automatically because >> there might be conflicting chips on the local bus that are unknown to >> the software, or that are just connected later. >> >> The alias pool and the mapping done at runtime allow to model >> different camera modules [or display or other modules] similarly to >> beaglebone capes or rpi hats, up to a model where: >> >> 1. there can be different camera modules being designed over time >> 2. there can be different base boards being designed over time >> 3. there is a standard interconnection between them (mechanical, >> electrical, communication bus) >> 4. camera modules and base boards are designed and sold independently >> (thanks to point 3) >> >> The implementation is split in the following patches: >> * Patch 1 adds the attach_client() and detach_client() callbacks to >> i2c-core >> * Patch 2 adds similar callbacks for the use of device drivers and, >> most importantly, implements the ATR engine >> * Patch 3 adds a farily complete DT bindings document, including the >> alias map >> * Patch 4 adds the DS90UB954-Q1 dual deserializer driver >> >> There is no serializer driver here. The one I have is just a skeleton >> setting a few registers, just enough to work on the deserializer >> driver. > > Not sure what to do here... I guess I'll just mark the patches as > RFC at media patchwork, as someone has to need support for it and need > to finish its implementation. I just did it. As I wrote in the cover letter, I was not actively working on the topic and sent these patches as an additional input for the discussion about I2C address translation and serdes chips in general.
Hi, there has been some discussion on linux-media about video serializer/deserializer chipsets with remote I2C capabilities from TI [0] and Maxim [1]. I took part discussing how the remote I2C feature of such chips could be best implemented in Linux while I was implementing a driver for the Texas Instruments DS90UB954-Q1 video deserializer. My approach is different from both the one used by Vladimir Zapolskiy on other TI chips, which look similar to the DS90UB954 in their I2C management, and the one used by Kieran Bingham with Maxim chips, which have a different and simpler I2C management. After that I had to stop that work, so it is unfinished and I have no plan to continue it. Upon suggestion by some linux-media developers I'm sending my patches as RFC in the hope that they bring additional material for the discussion. I2C management is quite complete in my patches, and it shows how I envisioned I2C management. For the rest the code is in large part incomplete. Don't consider the V4L2, GPIO and other sections as ready for any review. The whole idea is structured around a central node, called the ATR (Address Translator). It is similar to an I2C mux except it changes the I2C addresses of transactions with an "alias" address for each remote chip. Patch 2 has a detailed description of this process. A typical setup looks like: Slave X @ 0x10 .-----. | .-----. | |---+---- B | CPU |--A--| ATR | `-----' | |---+---- C `-----' | Slave Y @ 0x10 A = "local" bus B = "remote" bus 0 C = "remote" bus 1 In patch 2 I enriched the i2c-mux to also act as an ATR. However the implementation grew larger than I desired, so now I think it would make sense to leave i2c-mux as is, and add a new i2c-atr.c which has ATR features without much of the MUX code. However the implementation would not change too much, so you can look at i2c-mux to see how I implemented the ATR. In the ATR (i2c-mux.c) I implemented the logic needed to remap slave addresses according to a table. Choosing appropriate aliases and filling that table is driver-specific, so in this case it is done by ds90ub954.c. The ATR driver needs to know when a new client appears on the remote bus to setup translation and when it gets disconnected to undo it. So I added a callback pair, attach_client and detach_client, from i2c-core to i2c-mux and from there to the ATR driver. When getting the callback the ATR driver chooses an alias to be used on the local bus for the new chip, configures the ATR (perhaps setting some registers) returns the alias back to the ATR which sill add the new chip-alias pair to its table. The ATR (i2c-mux) then will do the translation for each message, so that the alias will be used on the local bus and the physical chip address on the remote bus. The alias address for a new client is chosen from an alias pool that must be defined in device tree. It is the responsibility of the DT writer to fill the pool with addresses that are otherwise unused on the local bus. The pool could not be filled automatically because there might be conflicting chips on the local bus that are unknown to the software, or that are just connected later. The alias pool and the mapping done at runtime allow to model different camera modules [or display or other modules] similarly to beaglebone capes or rpi hats, up to a model where: 1. there can be different camera modules being designed over time 2. there can be different base boards being designed over time 3. there is a standard interconnection between them (mechanical, electrical, communication bus) 4. camera modules and base boards are designed and sold independently (thanks to point 3) The implementation is split in the following patches: * Patch 1 adds the attach_client() and detach_client() callbacks to i2c-core * Patch 2 adds similar callbacks for the use of device drivers and, most importantly, implements the ATR engine * Patch 3 adds a farily complete DT bindings document, including the alias map * Patch 4 adds the DS90UB954-Q1 dual deserializer driver There is no serializer driver here. The one I have is just a skeleton setting a few registers, just enough to work on the deserializer driver. Each patch has an comprehensive list of open issues. [0] https://www.spinics.net/lists/linux-gpio/msg33291.html [1] https://www.spinics.net/lists/linux-media/msg142367.html Regards, -- Luca Luca Ceresoli (4): i2c: core: let adapters be notified of client attach/detach i2c: mux: notify client attach/detach, add ATR media: dt-bindings: add DS90UB954-Q1 video deserializer media: ds90ub954: new driver for TI DS90UB954-Q1 video deserializer .../bindings/media/ti,ds90ub954-q1.txt | 151 ++ drivers/i2c/i2c-core-base.c | 16 + drivers/i2c/i2c-mux.c | 218 ++- drivers/i2c/muxes/i2c-mux-pca954x.c | 2 +- drivers/media/Kconfig | 1 + drivers/media/Makefile | 2 +- drivers/media/serdes/Kconfig | 13 + drivers/media/serdes/Makefile | 1 + drivers/media/serdes/ds90ub954.c | 1335 +++++++++++++++++ include/linux/i2c-mux.h | 20 +- include/linux/i2c.h | 9 + 11 files changed, 1760 insertions(+), 8 deletions(-) create mode 100644 Documentation/devicetree/bindings/media/ti,ds90ub954-q1.txt create mode 100644 drivers/media/serdes/Kconfig create mode 100644 drivers/media/serdes/Makefile create mode 100644 drivers/media/serdes/ds90ub954.c