counter: stm32-timer-cnt: fix ceiling miss-alignment with reload register

BugLink: https://bugs.launchpad.net/bugs/1926489
commit b14d72ac731753708a7c1a6b3657b9312b6f0042 upstream

Ceiling value may be miss-aligned with what's actually configured into the
ARR register. This is seen after probe as currently the ARR value is zero,
whereas ceiling value is set to the maximum. So:
- reading ceiling reports zero
- in case the counter gets enabled without any prior configuration,
  it won't count.
- in case the function gets set by the user 1st, (priv->ceiling) is used.

Fix it by getting rid of the cached "priv->ceiling" variable. Rather use
the ARR register value directly by using regmap read or write when needed.
There should be no drawback on performance as priv->ceiling isn't used in
performance critical path.
There's also no point in writing ARR while setting function (sms), so
it can be safely removed.

Fixes: ad29937e206f ("counter: Add STM32 Timer quadrature encoder")
Suggested-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1614793789-10346-1-git-send-email-fabrice.gasnier@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
[sudip: adjuct context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/counter/stm32-timer-cnt.c b/drivers/counter/stm32-timer-cnt.c
index 75e08a98d09be6ec56886d8a14418c649ef2ccc0..889ea7a6ed630cd48b820ab2e4eb3ef8209fd45e 100644 (file)
--- a/drivers/counter/stm32-timer-cnt.c
+++ b/drivers/counter/stm32-timer-cnt.c
@@ -24,7 +24,6 @@ struct stm32_timer_cnt {
        struct counter_device counter;
        struct regmap *regmap;
        struct clk *clk;
-       u32 ceiling;
        u32 max_arr;
 };
 
@@ -67,14 +66,15 @@ static int stm32_count_write(struct counter_device *counter,
                             struct counter_count_write_value *val)
 {
        struct stm32_timer_cnt *const priv = counter->priv;
-       u32 cnt;
+       u32 cnt, ceiling;
        int err;
 
        err = counter_count_write_value_get(&cnt, COUNTER_COUNT_POSITION, val);
        if (err)
                return err;
 
-       if (cnt > priv->ceiling)
+       regmap_read(priv->regmap, TIM_ARR, &ceiling);
+       if (cnt > ceiling)
                return -EINVAL;
 
        return regmap_write(priv->regmap, TIM_CNT, cnt);
@@ -136,10 +136,6 @@ static int stm32_count_function_set(struct counter_device *counter,
 
        regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_CEN, 0);
 
-       /* TIMx_ARR register shouldn't be buffered (ARPE=0) */
-       regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_ARPE, 0);
-       regmap_write(priv->regmap, TIM_ARR, priv->ceiling);
-
        regmap_update_bits(priv->regmap, TIM_SMCR, TIM_SMCR_SMS, sms);
 
        /* Make sure that registers are updated */
@@ -197,7 +193,6 @@ static ssize_t stm32_count_ceiling_write(struct counter_device *counter,
        regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_ARPE, 0);
        regmap_write(priv->regmap, TIM_ARR, ceiling);
 
-       priv->ceiling = ceiling;
        return len;
 }
 
@@ -369,7 +364,6 @@ static int stm32_timer_cnt_probe(struct platform_device *pdev)
 
        priv->regmap = ddata->regmap;
        priv->clk = ddata->clk;
-       priv->ceiling = ddata->max_arr;
        priv->max_arr = ddata->max_arr;
 
        priv->counter.name = dev_name(dev);