| Message ID | 20240904-pci-qcom-gen4-stability-v6-4-ec39f7ae3f62@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | PCI: qcom: Add 16.0 GT/s equalization and margining settings | expand |
On Wed, Sep 04, 2024 at 12:42:00PM +0530, Manivannan Sadhasivam via B4 Relay wrote: > From: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com> > > Add RX lane margining settings for 16.0 GT/s (GEN 4) data rate. These > settings improve link stability while operating at high date rates and > helps to improve signal quality. > > Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com> > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > [mani: dropped the code refactoring and minor changes] > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > --- > drivers/pci/controller/dwc/pcie-designware.h | 18 ++++++++++++++++ > drivers/pci/controller/dwc/pcie-qcom-common.c | 31 +++++++++++++++++++++++++++ > drivers/pci/controller/dwc/pcie-qcom-common.h | 1 + > drivers/pci/controller/dwc/pcie-qcom-ep.c | 4 +++- > drivers/pci/controller/dwc/pcie-qcom.c | 4 +++- > 5 files changed, 56 insertions(+), 2 deletions(-) > > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h > index 51744ad25575..f5be99731f7e 100644 > --- a/drivers/pci/controller/dwc/pcie-designware.h > +++ b/drivers/pci/controller/dwc/pcie-designware.h > @@ -209,6 +209,24 @@ > > #define PCIE_PL_CHK_REG_ERR_ADDR 0xB28 > > +/* > + * 16.0 GT/s (GEN4) lane margining register definitions nit: Gen 4? > + */ > +#define GEN4_LANE_MARGINING_1_OFF 0xb80 nit: upper case hex > +#define MARGINING_MAX_VOLTAGE_OFFSET GENMASK(29, 24) > +#define MARGINING_NUM_VOLTAGE_STEPS GENMASK(22, 16) > +#define MARGINING_MAX_TIMING_OFFSET GENMASK(13, 8) > +#define MARGINING_NUM_TIMING_STEPS GENMASK(5, 0) > + > +#define GEN4_LANE_MARGINING_2_OFF 0xb84 Same here > +#define MARGINING_IND_ERROR_SAMPLER BIT(28) > +#define MARGINING_SAMPLE_REPORTING_METHOD BIT(27) > +#define MARGINING_IND_LEFT_RIGHT_TIMING BIT(26) > +#define MARGINING_IND_UP_DOWN_VOLTAGE BIT(25) > +#define MARGINING_VOLTAGE_SUPPORTED BIT(24) > +#define MARGINING_MAXLANES GENMASK(20, 16) > +#define MARGINING_SAMPLE_RATE_TIMING GENMASK(13, 8) > +#define MARGINING_SAMPLE_RATE_VOLTAGE GENMASK(5, 0) > /* > * iATU Unroll-specific register definitions > * From 4.80 core version the address translation will be made by unroll > diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.c b/drivers/pci/controller/dwc/pcie-qcom-common.c > index dc7d93db9dc5..99b75e7f085d 100644 > --- a/drivers/pci/controller/dwc/pcie-qcom-common.c > +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c > @@ -43,3 +43,34 @@ void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci) > dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg); > } > EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_eq_settings); > + > +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci) I'd try to find a shorter symbol name here, "settings" seems redundant after "set". Perhaps just qcom_pcie_common_enable_lane_margining() or qcom_pcie_common_enable_16gt_lane_margining()? if these settings are indeed specific to 16 GT/s. But perhaps it's better to let the helper honour pci->max_link_speed if different settings will later be needed for higher speeds: if (pcie_link_speed[pci->max_link_speed] >= PCIE_SPEED_16_0GT) qcom_pcie_common_enable_lane_margining(pci) > void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci); > +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci); And maybe something similar for the eq settings for symmetry. Johan
On Wed, Sep 04, 2024 at 11:53:42AM +0200, Johan Hovold wrote: > On Wed, Sep 04, 2024 at 12:42:00PM +0530, Manivannan Sadhasivam via B4 Relay wrote: > > From: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com> > > > > Add RX lane margining settings for 16.0 GT/s (GEN 4) data rate. These > > settings improve link stability while operating at high date rates and > > helps to improve signal quality. > > > > Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com> > > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > > [mani: dropped the code refactoring and minor changes] > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > > --- > > drivers/pci/controller/dwc/pcie-designware.h | 18 ++++++++++++++++ > > drivers/pci/controller/dwc/pcie-qcom-common.c | 31 +++++++++++++++++++++++++++ > > drivers/pci/controller/dwc/pcie-qcom-common.h | 1 + > > drivers/pci/controller/dwc/pcie-qcom-ep.c | 4 +++- > > drivers/pci/controller/dwc/pcie-qcom.c | 4 +++- > > 5 files changed, 56 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h > > index 51744ad25575..f5be99731f7e 100644 > > --- a/drivers/pci/controller/dwc/pcie-designware.h > > +++ b/drivers/pci/controller/dwc/pcie-designware.h > > @@ -209,6 +209,24 @@ > > > > #define PCIE_PL_CHK_REG_ERR_ADDR 0xB28 > > > > +/* > > + * 16.0 GT/s (GEN4) lane margining register definitions > > nit: Gen 4? > > > + */ > > +#define GEN4_LANE_MARGINING_1_OFF 0xb80 > > nit: upper case hex > > > +#define MARGINING_MAX_VOLTAGE_OFFSET GENMASK(29, 24) > > +#define MARGINING_NUM_VOLTAGE_STEPS GENMASK(22, 16) > > +#define MARGINING_MAX_TIMING_OFFSET GENMASK(13, 8) > > +#define MARGINING_NUM_TIMING_STEPS GENMASK(5, 0) > > + > > +#define GEN4_LANE_MARGINING_2_OFF 0xb84 > > Same here > > > +#define MARGINING_IND_ERROR_SAMPLER BIT(28) > > +#define MARGINING_SAMPLE_REPORTING_METHOD BIT(27) > > +#define MARGINING_IND_LEFT_RIGHT_TIMING BIT(26) > > +#define MARGINING_IND_UP_DOWN_VOLTAGE BIT(25) > > +#define MARGINING_VOLTAGE_SUPPORTED BIT(24) > > +#define MARGINING_MAXLANES GENMASK(20, 16) > > +#define MARGINING_SAMPLE_RATE_TIMING GENMASK(13, 8) > > +#define MARGINING_SAMPLE_RATE_VOLTAGE GENMASK(5, 0) > > /* > > * iATU Unroll-specific register definitions > > * From 4.80 core version the address translation will be made by unroll > > diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.c b/drivers/pci/controller/dwc/pcie-qcom-common.c > > index dc7d93db9dc5..99b75e7f085d 100644 > > --- a/drivers/pci/controller/dwc/pcie-qcom-common.c > > +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c > > @@ -43,3 +43,34 @@ void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci) > > dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg); > > } > > EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_eq_settings); > > + > > +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci) > > I'd try to find a shorter symbol name here, "settings" seems redundant > after "set". Perhaps just > > qcom_pcie_common_enable_lane_margining() > > or > > qcom_pcie_common_enable_16gt_lane_margining()? > This one looks better. Since lane margining is implemented in the receiver, we don't really need 'rx' in the function name. > if these settings are indeed specific to 16 GT/s. But perhaps it's > better to let the helper honour pci->max_link_speed if different > settings will later be needed for higher speeds: > > if (pcie_link_speed[pci->max_link_speed] >= PCIE_SPEED_16_0GT) > qcom_pcie_common_enable_lane_margining(pci) > I did thought about it during the review, but this setting claims to be for 16 GT/s only. So I wouldn't recommend applying it to other speeds without checking with Qcom. Unfortunately, I'm on vacation for 2 weeks and have limited access to Qcom internal docs/chat. So won't be able to check it soon. If Shashank could check it, it is fine. But on the conservative side, let's stick to 16 GT/s only? - Mani > > void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci); > > +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci); > > And maybe something similar for the eq settings for symmetry. > > Johan
On 9/4/24 09:04, Manivannan Sadhasivam wrote: > On Wed, Sep 04, 2024 at 11:53:42AM +0200, Johan Hovold wrote: >> On Wed, Sep 04, 2024 at 12:42:00PM +0530, Manivannan Sadhasivam via B4 Relay wrote: >>> From: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com> >>> >>> Add RX lane margining settings for 16.0 GT/s (GEN 4) data rate. These >>> settings improve link stability while operating at high date rates and >>> helps to improve signal quality. >>> >>> Signed-off-by: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com> >>> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> >>> [mani: dropped the code refactoring and minor changes] >>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> >>> --- >>> drivers/pci/controller/dwc/pcie-designware.h | 18 ++++++++++++++++ >>> drivers/pci/controller/dwc/pcie-qcom-common.c | 31 +++++++++++++++++++++++++++ >>> drivers/pci/controller/dwc/pcie-qcom-common.h | 1 + >>> drivers/pci/controller/dwc/pcie-qcom-ep.c | 4 +++- >>> drivers/pci/controller/dwc/pcie-qcom.c | 4 +++- >>> 5 files changed, 56 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h >>> index 51744ad25575..f5be99731f7e 100644 >>> --- a/drivers/pci/controller/dwc/pcie-designware.h >>> +++ b/drivers/pci/controller/dwc/pcie-designware.h >>> @@ -209,6 +209,24 @@ >>> >>> #define PCIE_PL_CHK_REG_ERR_ADDR 0xB28 >>> >>> +/* >>> + * 16.0 GT/s (GEN4) lane margining register definitions >> >> nit: Gen 4? >> >>> + */ >>> +#define GEN4_LANE_MARGINING_1_OFF 0xb80 >> >> nit: upper case hex >> >>> +#define MARGINING_MAX_VOLTAGE_OFFSET GENMASK(29, 24) >>> +#define MARGINING_NUM_VOLTAGE_STEPS GENMASK(22, 16) >>> +#define MARGINING_MAX_TIMING_OFFSET GENMASK(13, 8) >>> +#define MARGINING_NUM_TIMING_STEPS GENMASK(5, 0) >>> + >>> +#define GEN4_LANE_MARGINING_2_OFF 0xb84 >> >> Same here >> >>> +#define MARGINING_IND_ERROR_SAMPLER BIT(28) >>> +#define MARGINING_SAMPLE_REPORTING_METHOD BIT(27) >>> +#define MARGINING_IND_LEFT_RIGHT_TIMING BIT(26) >>> +#define MARGINING_IND_UP_DOWN_VOLTAGE BIT(25) >>> +#define MARGINING_VOLTAGE_SUPPORTED BIT(24) >>> +#define MARGINING_MAXLANES GENMASK(20, 16) >>> +#define MARGINING_SAMPLE_RATE_TIMING GENMASK(13, 8) >>> +#define MARGINING_SAMPLE_RATE_VOLTAGE GENMASK(5, 0) >>> /* >>> * iATU Unroll-specific register definitions >>> * From 4.80 core version the address translation will be made by unroll >>> diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.c b/drivers/pci/controller/dwc/pcie-qcom-common.c >>> index dc7d93db9dc5..99b75e7f085d 100644 >>> --- a/drivers/pci/controller/dwc/pcie-qcom-common.c >>> +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c >>> @@ -43,3 +43,34 @@ void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci) >>> dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg); >>> } >>> EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_eq_settings); >>> + >>> +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci) >> >> I'd try to find a shorter symbol name here, "settings" seems redundant >> after "set". Perhaps just >> >> qcom_pcie_common_enable_lane_margining() >> >> or >> >> qcom_pcie_common_enable_16gt_lane_margining()? >> > > This one looks better. Since lane margining is implemented in the receiver, we > don't really need 'rx' in the function name. > >> if these settings are indeed specific to 16 GT/s. But perhaps it's >> better to let the helper honour pci->max_link_speed if different >> settings will later be needed for higher speeds: >> >> if (pcie_link_speed[pci->max_link_speed] >= PCIE_SPEED_16_0GT) >> qcom_pcie_common_enable_lane_margining(pci) >> > > I did thought about it during the review, but this setting claims to be for 16 > GT/s only. So I wouldn't recommend applying it to other speeds without checking > with Qcom. > > Unfortunately, I'm on vacation for 2 weeks and have limited access to Qcom > internal docs/chat. So won't be able to check it soon. If Shashank could check > it, it is fine. But on the conservative side, let's stick to 16 GT/s only? > > - Mani Yes Mani I think we have to stick to 16 GT/s only for now as we haven't characterized 32 GT/s yet. > >>> void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci); >>> +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci); >> >> And maybe something similar for the eq settings for symmetry. >> >> Johan >
On Wed, Sep 04, 2024 at 01:48:09PM -0700, Shashank Babu Chinta Venkata wrote: > On 9/4/24 09:04, Manivannan Sadhasivam wrote: > > On Wed, Sep 04, 2024 at 11:53:42AM +0200, Johan Hovold wrote: > >> On Wed, Sep 04, 2024 at 12:42:00PM +0530, Manivannan Sadhasivam via B4 Relay wrote: > >>> From: Shashank Babu Chinta Venkata <quic_schintav@quicinc.com> > >>> +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci) > >> > >> I'd try to find a shorter symbol name here, "settings" seems redundant > >> after "set". Perhaps just > >> > >> qcom_pcie_common_enable_lane_margining() > >> > >> or > >> > >> qcom_pcie_common_enable_16gt_lane_margining()? > >> > > > > This one looks better. Since lane margining is implemented in the receiver, we > > don't really need 'rx' in the function name. > > > >> if these settings are indeed specific to 16 GT/s. But perhaps it's > >> better to let the helper honour pci->max_link_speed if different > >> settings will later be needed for higher speeds: > >> > >> if (pcie_link_speed[pci->max_link_speed] >= PCIE_SPEED_16_0GT) > >> qcom_pcie_common_enable_lane_margining(pci) > >> > > > > I did thought about it during the review, but this setting claims to be for 16 > > GT/s only. So I wouldn't recommend applying it to other speeds without checking > > with Qcom. Yeah, this was more an example of what the code may look like eventually since IIUC anything above Gen4 will need lane margining. > > Unfortunately, I'm on vacation for 2 weeks and have limited access to Qcom > > internal docs/chat. So won't be able to check it soon. If Shashank could check > > it, it is fine. But on the conservative side, let's stick to 16 GT/s only? > Yes Mani I think we have to stick to 16 GT/s only for now as we > haven't characterized 32 GT/s yet. Sounds good. We can always generalise or rename these functions later (e.g. when adding support for higher speeds). > >>> void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci); > >>> +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci); Perhaps just dropping "_settings" (and replacing "_rx") is enough for now? So something like: qcom_pcie_common_set_16gt_equalization() qcom_pcie_common_set_16gt_lane_margining() A bit shorter and pretty self-explaining. Johan
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h index 51744ad25575..f5be99731f7e 100644 --- a/drivers/pci/controller/dwc/pcie-designware.h +++ b/drivers/pci/controller/dwc/pcie-designware.h @@ -209,6 +209,24 @@ #define PCIE_PL_CHK_REG_ERR_ADDR 0xB28 +/* + * 16.0 GT/s (GEN4) lane margining register definitions + */ +#define GEN4_LANE_MARGINING_1_OFF 0xb80 +#define MARGINING_MAX_VOLTAGE_OFFSET GENMASK(29, 24) +#define MARGINING_NUM_VOLTAGE_STEPS GENMASK(22, 16) +#define MARGINING_MAX_TIMING_OFFSET GENMASK(13, 8) +#define MARGINING_NUM_TIMING_STEPS GENMASK(5, 0) + +#define GEN4_LANE_MARGINING_2_OFF 0xb84 +#define MARGINING_IND_ERROR_SAMPLER BIT(28) +#define MARGINING_SAMPLE_REPORTING_METHOD BIT(27) +#define MARGINING_IND_LEFT_RIGHT_TIMING BIT(26) +#define MARGINING_IND_UP_DOWN_VOLTAGE BIT(25) +#define MARGINING_VOLTAGE_SUPPORTED BIT(24) +#define MARGINING_MAXLANES GENMASK(20, 16) +#define MARGINING_SAMPLE_RATE_TIMING GENMASK(13, 8) +#define MARGINING_SAMPLE_RATE_VOLTAGE GENMASK(5, 0) /* * iATU Unroll-specific register definitions * From 4.80 core version the address translation will be made by unroll diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.c b/drivers/pci/controller/dwc/pcie-qcom-common.c index dc7d93db9dc5..99b75e7f085d 100644 --- a/drivers/pci/controller/dwc/pcie-qcom-common.c +++ b/drivers/pci/controller/dwc/pcie-qcom-common.c @@ -43,3 +43,34 @@ void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci) dw_pcie_writel_dbi(pci, GEN3_EQ_CONTROL_OFF, reg); } EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_eq_settings); + +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci) +{ + u32 reg; + + reg = dw_pcie_readl_dbi(pci, GEN4_LANE_MARGINING_1_OFF); + reg &= ~(MARGINING_MAX_VOLTAGE_OFFSET | + MARGINING_NUM_VOLTAGE_STEPS | + MARGINING_MAX_TIMING_OFFSET | + MARGINING_NUM_TIMING_STEPS); + reg |= FIELD_PREP(MARGINING_MAX_VOLTAGE_OFFSET, 0x24) | + FIELD_PREP(MARGINING_NUM_VOLTAGE_STEPS, 0x78) | + FIELD_PREP(MARGINING_MAX_TIMING_OFFSET, 0x32) | + FIELD_PREP(MARGINING_NUM_TIMING_STEPS, 0x10); + dw_pcie_writel_dbi(pci, GEN4_LANE_MARGINING_1_OFF, reg); + + reg = dw_pcie_readl_dbi(pci, GEN4_LANE_MARGINING_2_OFF); + reg |= MARGINING_IND_ERROR_SAMPLER | + MARGINING_SAMPLE_REPORTING_METHOD | + MARGINING_IND_LEFT_RIGHT_TIMING | + MARGINING_VOLTAGE_SUPPORTED; + reg &= ~(MARGINING_IND_UP_DOWN_VOLTAGE | + MARGINING_MAXLANES | + MARGINING_SAMPLE_RATE_TIMING | + MARGINING_SAMPLE_RATE_VOLTAGE); + reg |= FIELD_PREP(MARGINING_MAXLANES, pci->num_lanes) | + FIELD_PREP(MARGINING_SAMPLE_RATE_TIMING, 0x3f) | + FIELD_PREP(MARGINING_SAMPLE_RATE_VOLTAGE, 0x3f); + dw_pcie_writel_dbi(pci, GEN4_LANE_MARGINING_2_OFF, reg); +} +EXPORT_SYMBOL_GPL(qcom_pcie_common_set_16gt_rx_margining_settings); diff --git a/drivers/pci/controller/dwc/pcie-qcom-common.h b/drivers/pci/controller/dwc/pcie-qcom-common.h index 259e04b7bdf9..e9ddc901082e 100644 --- a/drivers/pci/controller/dwc/pcie-qcom-common.h +++ b/drivers/pci/controller/dwc/pcie-qcom-common.h @@ -6,3 +6,4 @@ #include "pcie-designware.h" void qcom_pcie_common_set_16gt_eq_settings(struct dw_pcie *pci); +void qcom_pcie_common_set_16gt_rx_margining_settings(struct dw_pcie *pci); diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c index af83470216e8..5c220f2ecafe 100644 --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c @@ -487,8 +487,10 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci) goto err_disable_resources; } - if (pcie_link_speed[pci->max_link_speed] == PCIE_SPEED_16_0GT) + if (pcie_link_speed[pci->max_link_speed] == PCIE_SPEED_16_0GT) { qcom_pcie_common_set_16gt_eq_settings(pci); + qcom_pcie_common_set_16gt_rx_margining_settings(pci); + } /* * The physical address of the MMIO region which is exposed as the BAR diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c index 2742e82fdcb3..b0b1d8d34279 100644 --- a/drivers/pci/controller/dwc/pcie-qcom.c +++ b/drivers/pci/controller/dwc/pcie-qcom.c @@ -284,8 +284,10 @@ static int qcom_pcie_start_link(struct dw_pcie *pci) { struct qcom_pcie *pcie = to_qcom_pcie(pci); - if (pcie_link_speed[pci->max_link_speed] == PCIE_SPEED_16_0GT) + if (pcie_link_speed[pci->max_link_speed] == PCIE_SPEED_16_0GT) { qcom_pcie_common_set_16gt_eq_settings(pci); + qcom_pcie_common_set_16gt_rx_margining_settings(pci); + } /* Enable Link Training state machine */ if (pcie->cfg->ops->ltssm_enable)