--- /dev/null
+From dab8f9f0fe3aada61c0eb013dcf7d3ff75a2c336 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@baylibre.com>
+Date: Fri, 21 Jun 2024 16:37:13 +0200
+Subject: pwm: stm32: Fix calculation of prescaler
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+From: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
+
+commit dab8f9f0fe3aada61c0eb013dcf7d3ff75a2c336 upstream.
+
+A small prescaler is beneficial, as this improves the resolution of the
+duty_cycle configuration. However if the prescaler is too small, the
+maximal possible period becomes considerably smaller than the requested
+value.
+
+One situation where this goes wrong is the following: With a parent
+clock rate of 208877930 Hz and max_arr = 0xffff = 65535, a request for
+period = 941243 ns currently results in PSC = 1. The value for ARR is
+then calculated to
+
+ ARR = 941243 * 208877930 / (1000000000 * 2) - 1 = 98301
+
+This value is bigger than 65535 however and so doesn't fit into the
+respective register field. In this particular case the PWM was
+configured for a period of 313733.4806027616 ns (with ARR = 98301 &
+0xffff). Even if ARR was configured to its maximal value, only period =
+627495.6861167669 ns would be achievable.
+
+Fix the calculation accordingly and adapt the comment to match the new
+algorithm.
+
+With the calculation fixed the above case results in PSC = 2 and so an
+actual period of 941229.1667195285 ns.
+
+Fixes: 8002fbeef1e4 ("pwm: stm32: Calculate prescaler with a division instead of a loop")
+Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
+Link: https://lore.kernel.org/r/b4d96b79917617434a540df45f20cb5de4142f88.1718979150.git.u.kleine-koenig@baylibre.com
+Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ drivers/pwm/pwm-stm32.c | 18 ++++++++++++------
+ 1 file changed, 12 insertions(+), 6 deletions(-)
+
+--- a/drivers/pwm/pwm-stm32.c
++++ b/drivers/pwm/pwm-stm32.c
+@@ -321,17 +321,23 @@ static int stm32_pwm_config(struct stm32
+ * First we need to find the minimal value for prescaler such that
+ *
+ * period_ns * clkrate
+- * ------------------------------
++ * ------------------------------ < max_arr + 1
+ * NSEC_PER_SEC * (prescaler + 1)
+ *
+- * isn't bigger than max_arr.
++ * This equation is equivalent to
++ *
++ * period_ns * clkrate
++ * ---------------------------- < prescaler + 1
++ * NSEC_PER_SEC * (max_arr + 1)
++ *
++ * Using integer division and knowing that the right hand side is
++ * integer, this is further equivalent to
++ *
++ * (period_ns * clkrate) // (NSEC_PER_SEC * (max_arr + 1)) ≤ prescaler
+ */
+
+ prescaler = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk),
+- (u64)NSEC_PER_SEC * priv->max_arr);
+- if (prescaler > 0)
+- prescaler -= 1;
+-
++ (u64)NSEC_PER_SEC * ((u64)priv->max_arr + 1));
+ if (prescaler > MAX_TIM_PSC)
+ return -EINVAL;
+
--- /dev/null
+From f01af3022d4a46362c5dda3d35dea939f3246d10 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@baylibre.com>
+Date: Fri, 21 Jun 2024 16:37:14 +0200
+Subject: pwm: stm32: Fix error message to not describe the previous error path
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+From: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
+
+commit f01af3022d4a46362c5dda3d35dea939f3246d10 upstream.
+
+"Failed to lock the clock" is an appropriate error message for
+clk_rate_exclusive_get() failing, but not for the clock running too
+fast for the driver's calculations.
+
+Adapt the error message accordingly.
+
+Fixes: d44d635635a7 ("pwm: stm32: Fix for settings using period > UINT32_MAX")
+Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
+Link: https://lore.kernel.org/r/285182163211203fc823a65b180761f46e828dcb.1718979150.git.u.kleine-koenig@baylibre.com
+Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ drivers/pwm/pwm-stm32.c | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+--- a/drivers/pwm/pwm-stm32.c
++++ b/drivers/pwm/pwm-stm32.c
+@@ -679,7 +679,8 @@ static int stm32_pwm_probe(struct platfo
+ * .apply() won't overflow.
+ */
+ if (clk_get_rate(priv->clk) > 1000000000)
+- return dev_err_probe(dev, -EINVAL, "Failed to lock clock\n");
++ return dev_err_probe(dev, -EINVAL, "Clock freq too high (%lu)\n",
++ clk_get_rate(priv->clk));
+
+ chip->ops = &stm32pwm_ops;
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
