From: Thierry Reding <thierry.reding@gmail.com>
To: Fabrice Gasnier <fabrice.gasnier@st.com>
Cc: stefan.wahren@i2se.com, gohai@sukzessiv.net,
hsweeten@visionengravers.com, gottfried.haider@gmail.com,
loic.pallardy@st.com, broonie@kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-rpi-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org
Subject: Re: [RESEND PATCH] Revert "pwm: Set class for exported channels in sysfs"
Date: Mon, 24 Sep 2018 16:23:18 +0200 [thread overview]
Message-ID: <20180924142318.GG23547@ulmo> (raw)
In-Reply-To: <fc02ced1-01ba-dde4-95da-285d9351338b@st.com>
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On Mon, Sep 24, 2018 at 03:59:03PM +0200, Fabrice Gasnier wrote:
> On 09/24/2018 01:53 PM, Thierry Reding wrote:
> > On Fri, Sep 21, 2018 at 04:02:47PM +0200, Fabrice Gasnier wrote:
> >> This reverts commit 7e5d1fd75c3dde9fc10c4472b9368089d1b81d00 as it causes
> >> regression with multiple pwm chip. It creates a new entry in
> >> '/sys/class/pwm' every time a 'pwmX' is exported with 'echo X > export':
> >> - 1st time export will create an entry in /sys/class/pwm/pwmX
> >> - when another export happens on another pwmchip, it can't be created
> >> (e.g. -EEXIST)
> >>
> >> This also changes existing ABI (Documentation/ABI/testing/sysfs-class-pwm):
> >> - pmwX should be there: /sys/class/pwm/pwmchipN/pwmX
> >>
> >> Example on stm32 (stm32429i-eval) platform:
> >> $ ls /sys/class/pwm
> >> pwmchip0 pwmchip4
> >>
> >> $ cd /sys/class/pwm/pwmchip0/
> >> $ echo 0 > export
> >> $ ls /sys/class/pwm
> >> pwm0 pwmchip0 pwmchip4
> >>
> >> $ cd /sys/class/pwm/pwmchip4/
> >> $ echo 0 > export
> >> sysfs: cannot create duplicate filename '/class/pwm/pwm0'
> >> ...Exception stack follows...
> >>
> >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
> >> ---
> >> drivers/pwm/sysfs.c | 1 -
> >> 1 file changed, 1 deletion(-)
> >
> > Can we come up with an alternative that allows us to have both? We want
> > uevent and proper sysfs creation, or is that not possible?
>
> Hi Thierry, all,
>
> With current approach:
> - "export->child.class = parent->class"
> - ABI (e.g. "pwm%d") device name isn't unique with multiple pwm chip.
> I think this is not possible.
>
> Trying to think of an alternative... I just did a quick test, by
> changing device name, to take pwmchip into account:
> + export->child.class = parent->class;
> export->child.release = pwm_export_release;
> export->child.parent = parent;
> export->child.devt = MKDEV(0, 0);
> export->child.groups = pwm_groups;
> - dev_set_name(&export->child, "pwm%u", pwm->hwpwm);
> + dev_set_name(&export->child, "pwmchip%d-pwm%u", chip->base,
> pwm->hwpwm);
>
> But this also impacts existing ABI :-(
> Would you have suggestions to send an uevent, without modifying ABI ?
I don't quite understand why, in the example you show in the commit
message, the pwmX nodes appear in the top-level /sys/class/pwm
directory. According to Documentation/ABI/testing/sysfs-class-pwm they
should appear as /sys/class/pwm/pwmchipN/pwmX. I can only imagine that
setting the class may have changed that. If so, perhaps we can
workaround that by creating a new class that is not parent->class?
Thierry
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next prev parent reply other threads:[~2018-09-24 14:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-21 14:02 [RESEND PATCH] Revert "pwm: Set class for exported channels in sysfs" Fabrice Gasnier
2018-09-24 11:53 ` Thierry Reding
2018-09-24 13:59 ` Fabrice Gasnier
2018-09-24 14:23 ` Thierry Reding [this message]
2018-09-24 15:50 ` Fabrice Gasnier
2018-09-25 13:59 ` Fabrice Gasnier
2018-09-25 15:20 ` Thierry Reding
2018-09-29 0:19 ` Gottfried Haider
2018-10-01 13:28 ` Fabrice Gasnier
-- strict thread matches above, loose matches on Subject: below --
2018-07-20 7:27 Fabrice Gasnier
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