On Wed, Aug 13, 2014 at 05:18:53PM +0200, Geert Uytterhoeven wrote:
> If pwm_get() finds a look-up entry with a perfect match (both dev_id and
> con_id match), the loop is aborted, and "p" still points to the correct
> struct pwm_lookup.
>
> If only an entry with a matching dev_id or con_id is found, the loop
> terminates after traversing the whole list, and "p" now points to
> arbitrary memory, not part of the pwm_lookup list.
> Then pwm_set_period() and pwm_set_polarity() will set random values for
> period resp. polarity.
>
> To fix this, save period and polarity when finding a new best match,
> just like is done for chip (for the provider) and index.
>
> This fixes the LCD backlight on r8a7740/armadillo-legacy, which was fed
> period 0 and polarity -1068821144 instead of 33333 resp. 1.
>
> Fixes: 3796ce1d4d4b330a75005c5eda105603ce9d4071 ("pwm: add period and polarity to struct pwm_lookup")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> drivers/pwm/core.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
Good catch! One comment below.
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 4b66bf09ee55..d2c35920ff08 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -606,6 +606,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
> unsigned int best = 0;
> struct pwm_lookup *p;
> unsigned int match;
> + unsigned int period;
> + enum pwm_polarity polarity;
>
> /* look up via DT first */
> if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
> @@ -653,6 +655,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
> if (match > best) {
> chip = pwmchip_find_by_name(p->provider);
> index = p->index;
> + period = p->period;
> + polarity = p->polarity;
>
> if (match != 3)
> best = match;
> @@ -668,8 +672,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
> if (IS_ERR(pwm))
> return pwm;
>
> - pwm_set_period(pwm, p->period);
> - pwm_set_polarity(pwm, p->polarity);
> + pwm_set_period(pwm, period);
> + pwm_set_polarity(pwm, polarity);
Could we achieve the same by storing a pointer to the best match and
then use that instead of p? Perhaps something like this:
struct pwm_lookup *entry;
...
if (match > best) {
chip = pwmchip_find_by_name(p->provider);
entry = p;
if (match != 3)
best = match;
else
break;
}
...
if (chip)
pwm = pwm_request_from_chip(chip, entry->index,
con_id ?: dev_id);
if (IS_ERR(pwm))
return pwm;
pwm_set_period(pwm, entry->period);
pwm_set_polarity(pwm, entry->polarity);
?
Thierry
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