[PATCH] pwm: Fix period and polarity in pwm_get() for non-perfect matches
From: Thierry Reding <hidden>
Date: 2014-08-18 08:20:47
Also in:
linux-omap, linux-pwm, linux-sh, lkml, stable
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@glider.be>
Cc: stable at vger.kernel.org
---
drivers/pwm/core.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)Good catch! One comment below.
quoted hunk ↗ jump to hunk
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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