[PATCH v4 0/3] leds: rgb: leds-qcom-lpg: PWM fixes

[PATCH v4 0/3] leds: rgb: leds-qcom-lpg: PWM fixes

[Abel Vesa]

The PWM allow configuring the PWM resolution from 8 bits PWM
values up to 15 bits values, for the Hi-Res PWMs, and then either
6-bit or 9-bit for the normal PWMs. The current implementation loops
through all possible resolutions (PWM sizes), for the PWM subtype, on top
of the already existing process of determining the prediv, exponent and
refclk.

The first and second issues are related to capping the computed PWM
value.

The third issue is that it uses the wrong maximum possible PWM
value for determining the best matched period.

Fix all of them.

Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
---
Changes in v4:
- Rebased on next-20250305
- Re-worded the commit messages for the first two patches to include an
  example that should better explain what the issue that is being fixed
  is. As per Uwe's request.
- Link to v3: https://lore.kernel.org/r/20250303-leds-qcom-lpg-fix-max-pwm-on-hi-res-v3-0-62703c0ab76a@linaro.org

Changes in v3:
- Added a new patch that fixes the normal PWMs, since they now support
  6-bit resolution as well. Added it as first patch.
- Re-worded the second patch. Included Bjorn's suggestion and R-b tag.
- Link to v2: https://lore.kernel.org/r/20250226-leds-qcom-lpg-fix-max-pwm-on-hi-res-v2-0-7af5ef5d220b@linaro.org

Changes in v2:
- Re-worded the commit to drop the details that are not important
  w.r.t. what the patch is fixing.
- Added another patch which fixes the resolution used for determining
  best matched period and PWM config.
- Link to v1: https://lore.kernel.org/r/20250220-leds-qcom-lpg-fix-max-pwm-on-hi-res-v1-1-a161ec670ea5@linaro.org

---
Abel Vesa (3):
      leds: rgb: leds-qcom-lpg: Fix pwm resolution max for normal PWMs
      leds: rgb: leds-qcom-lpg: Fix pwm resolution max for Hi-Res PWMs
      leds: rgb: leds-qcom-lpg: Fix calculation of best period Hi-Res PWMs

 drivers/leds/rgb/leds-qcom-lpg.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
---
base-commit: 7ec162622e66a4ff886f8f28712ea1b13069e1aa
change-id: 20250220-leds-qcom-lpg-fix-max-pwm-on-hi-res-067e8782a79b

Best regards,
-- 
Abel Vesa <abel.vesa@linaro.org>

[PATCH v4 1/3] leds: rgb: leds-qcom-lpg: Fix pwm resolution max for normal PWMs

[Abel Vesa]

Ideally, the requested duty cycle should never translate to a PWM
value higher than the selected resolution (PWM size), but currently the
best matched period is never reported back to the PWM consumer, so the
consumer will still be using the requested period which is higher than
the best matched one. This will result in PWM consumer requesting
duty cycle values higher than the allowed PWM value.

For example, a consumer might request a period of 5ms while the best
(closest) period the PWM hardware will do is 4.26ms. For this best
matched resolution, if the selected resolution is 9-bit wide, when
the consumer asks for a duty cycle of 5ms, the PWM value will be 600,
which is outside of what the resolution allows. Similar will happen
if the 6-bit resolution is selected.

Since for these normal PWMs (non Hi-Res), the current implementation is
capping the PWM value at a 9-bit resolution, even when the 6-bit
resolution is selected, the value will be wrapped around to 6-bit value
by the HW internal logic.

Fix the issue by capping the PWM value to the maximum value allowed by
the selected resolution.

Fixes: 7a3350495d9a ("leds: rgb: leds-qcom-lpg: Add support for 6-bit PWM resolution")
Suggested-by: Anjelique Melendez <anjelique.melendez@oss.qualcomm.com>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
---
 drivers/leds/rgb/leds-qcom-lpg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
index 4e5c56ded1f0412c9913670699e912b24f3408bd..4454fc6a38480b61916318dd170f3eddc32976d6 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -533,7 +533,7 @@ static void lpg_calc_duty(struct lpg_channel *chan, uint64_t duty)
 		max = LPG_RESOLUTION_15BIT - 1;
 		clk_rate = lpg_clk_rates_hi_res[chan->clk_sel];
 	} else {
-		max = LPG_RESOLUTION_9BIT - 1;
+		max = BIT(lpg_pwm_resolution[chan->pwm_resolution_sel]) - 1;
 		clk_rate = lpg_clk_rates[chan->clk_sel];
 	}
 

-- 
2.34.1

[PATCH v4 2/3] leds: rgb: leds-qcom-lpg: Fix pwm resolution max for Hi-Res PWMs

[Abel Vesa]

Ideally, the requested duty cycle should never translate to a PWM
value higher than the selected resolution (PWM size), but currently the
best matched period is never reported back to the PWM consumer, so the
consumer will still be using the requested period which is higher than
the best matched one. This will result in PWM consumer requesting
duty cycle values higher than the allowed PWM value.

For example, a consumer might request a period of 5ms while the best
(closest) period the PWM hardware will do is 4.26ms. For this best
matched resolution, if the selected resolution is 8-bit wide, when
the consumer asks for a duty cycle of 5ms, the PWM value will be 300,
which is outside of what the resolution allows. This will happen with
all possible resolutions when selected.

Since for these Hi-Res PWMs, the current implementation is capping the PWM
value at a 15-bit resolution, even when lower resolutions are selected,
the value will be wrapped around by the HW internal logic to the selected
resolution.

Fix the issue by capping the PWM value to the maximum value allowed by
the selected resolution.

Cc: stable@vger.kernel.org    # 6.4
Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
---
 drivers/leds/rgb/leds-qcom-lpg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
index 4454fc6a38480b61916318dd170f3eddc32976d6..0b6310184988c299d82ee7181982c03d306407a4 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -530,7 +530,7 @@ static void lpg_calc_duty(struct lpg_channel *chan, uint64_t duty)
 	unsigned int clk_rate;
 
 	if (chan->subtype == LPG_SUBTYPE_HI_RES_PWM) {
-		max = LPG_RESOLUTION_15BIT - 1;
+		max = BIT(lpg_pwm_resolution_hi_res[chan->pwm_resolution_sel]) - 1;
 		clk_rate = lpg_clk_rates_hi_res[chan->clk_sel];
 	} else {
 		max = BIT(lpg_pwm_resolution[chan->pwm_resolution_sel]) - 1;

-- 
2.34.1

[PATCH v4 3/3] leds: rgb: leds-qcom-lpg: Fix calculation of best period Hi-Res PWMs

[Abel Vesa]

When determining the actual best period by looping through all
possible PWM configs, the resolution currently used is based on
bit shift value which is off-by-one above the possible maximum
PWM value allowed.

So subtract one from the resolution before determining the best
period so that the maximum duty cycle requested by the PWM user
won't result in a value above the maximum allowed by the selected
resolution.

Cc: stable@vger.kernel.org    # 6.4
Fixes: b00d2ed37617 ("leds: rgb: leds-qcom-lpg: Add support for high resolution PWM")
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
---
 drivers/leds/rgb/leds-qcom-lpg.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/leds/rgb/leds-qcom-lpg.c b/drivers/leds/rgb/leds-qcom-lpg.c
index 0b6310184988c299d82ee7181982c03d306407a4..4f2a178e3d265a2cc88e651d3e2ca6ae3dfac2e2 100644
--- a/drivers/leds/rgb/leds-qcom-lpg.c
+++ b/drivers/leds/rgb/leds-qcom-lpg.c
@@ -462,7 +462,7 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
 		max_res = LPG_RESOLUTION_9BIT;
 	}
 
-	min_period = div64_u64((u64)NSEC_PER_SEC * (1 << pwm_resolution_arr[0]),
+	min_period = div64_u64((u64)NSEC_PER_SEC * ((1 << pwm_resolution_arr[0]) - 1),
 			       clk_rate_arr[clk_len - 1]);
 	if (period <= min_period)
 		return -EINVAL;
@@ -483,7 +483,7 @@ static int lpg_calc_freq(struct lpg_channel *chan, uint64_t period)
 	 */
 
 	for (i = 0; i < pwm_resolution_count; i++) {
-		resolution = 1 << pwm_resolution_arr[i];
+		resolution = (1 << pwm_resolution_arr[i]) - 1;
 		for (clk_sel = 1; clk_sel < clk_len; clk_sel++) {
 			u64 numerator = period * clk_rate_arr[clk_sel];
 
@@ -1292,7 +1292,7 @@ static int lpg_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 		if (ret)
 			return ret;
 
-		state->period = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * (1 << resolution) *
+		state->period = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * ((1 << resolution) - 1) *
 						 pre_div * (1 << m), refclk);
 		state->duty_cycle = DIV_ROUND_UP_ULL((u64)NSEC_PER_SEC * pwm_value * pre_div * (1 << m), refclk);
 	} else {

-- 
2.34.1

Re: [PATCH v4 0/3] leds: rgb: leds-qcom-lpg: PWM fixes

[Lee Jones]

On Wed, 05 Mar 2025 15:09:03 +0200, Abel Vesa wrote:
> The PWM allow configuring the PWM resolution from 8 bits PWM
> values up to 15 bits values, for the Hi-Res PWMs, and then either
> 6-bit or 9-bit for the normal PWMs. The current implementation loops
> through all possible resolutions (PWM sizes), for the PWM subtype, on top
> of the already existing process of determining the prediv, exponent and
> refclk.
> 
> [...]

Applied, thanks!

[1/3] leds: rgb: leds-qcom-lpg: Fix pwm resolution max for normal PWMs
      commit: d3fd20cecf7fcdada938429ad525daf5b2217a7a
[2/3] leds: rgb: leds-qcom-lpg: Fix pwm resolution max for Hi-Res PWMs
      commit: 638fc32c056aa62c7add071205de6acc479ee37d
[3/3] leds: rgb: leds-qcom-lpg: Fix calculation of best period Hi-Res PWMs
      commit: 227fc065ae9e707af9c7d346458f43fd25cf310a

--
Lee Jones [李琼斯]