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Fri, 22 May 2026 12:14:18 -0700 (PDT) From: Ronaldo Nunez To: linux-pwm@vger.kernel.org Cc: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Ronaldo Nunez Subject: [PATCH v2] pwm: imx27: Fix variable truncation in .apply() Date: Fri, 22 May 2026 16:13:48 -0300 Message-ID: <20260522191348.6227-1-rnunez@baylibre.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Fix a variable truncation when calculating period in microseconds as part of the solution for the ERR051198 in .apply() callback. Example scenario: - Period of 3us (PWMPR = 196 and prescaler = 1) - Expected value in tmp: 198000000000 (NSEC_PER_SEC * (196 + 2) * 1) - Actual value is 431504384 (truncation to u32) Signed-off-by: Ronaldo Nunez --- Changes in v2: - Added example with actual PWMPR/prescaler values per Frank Li's feedback - Dropped testing section --- drivers/pwm/pwm-imx27.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index 3d34cdc4a3a5..c8b801fcb525 100644 --- a/drivers/pwm/pwm-imx27.c +++ b/drivers/pwm/pwm-imx27.c @@ -200,7 +200,7 @@ static void pwm_imx27_wait_fifo_slot(struct pwm_chip *chip, static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, const struct pwm_state *state) { - unsigned long period_cycles, duty_cycles, prescale, period_us, tmp; + unsigned long period_cycles, duty_cycles, prescale, period_us; struct pwm_imx27_chip *imx = to_pwm_imx27_chip(chip); unsigned long long c; unsigned long long clkrate; @@ -208,6 +208,7 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, int val; int ret; u32 cr; + u64 tmp; clkrate = clk_get_rate(imx->clks[PWM_IMX27_PER].clk); c = clkrate * state->period; @@ -249,6 +250,11 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, val = readl(imx->mmio_base + MX3_PWMPR); val = val >= MX3_PWMPR_MAX ? MX3_PWMPR_MAX : val; cr = readl(imx->mmio_base + MX3_PWMCR); + + /* + * tmp stores period in nanoseconds. Result fits in u64 since + * val <= 0xfffe and prescaler in [1, 0x1000]. + */ tmp = NSEC_PER_SEC * (u64)(val + 2) * MX3_PWMCR_PRESCALER_GET(cr); tmp = DIV_ROUND_UP_ULL(tmp, clkrate); period_us = DIV_ROUND_UP_ULL(tmp, 1000); -- 2.53.0