linux-kernel - Re: [PATCH v3] regmap: add iopoll-like atomic polling macro

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Date:   Thu, 9 Jan 2020 16:57:53 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sameer Pujar <spujar@...dia.com>, broonie@...nel.org
Cc:     jonathanh@...dia.com, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3] regmap: add iopoll-like atomic polling macro

09.01.2020 10:24, Sameer Pujar пишет:
> 
> On 1/9/2020 11:30 AM, Dmitry Osipenko wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 09.01.2020 08:09, Sameer Pujar пишет:
>>> This patch adds a macro 'regmap_read_poll_timeout_atomic' that works
>>> similar to 'readx_poll_timeout_atomic' defined in linux/iopoll.h; This
>>> is atomic version of already available 'regmap_read_poll_timeout' macro.
>>>
>>> It should be noted that above atomic macro cannot be used by all
>>> regmaps.
>>> If the regmap is set up for atomic use (flat or no cache and MMIO) then
>>> only it can use.
>>>
>>> Signed-off-by: Sameer Pujar <spujar@...dia.com>
>>> ---
>> Could you please explain what is the targeted use-case here?
> 
> I was trying to use regmap_read_poll_timeout() to poll for status change
> of a register. This resulted in "BUG: scheduling while atomic". The
> callback function, in which I was trying to use the macro, runs in
> atomic context. Hence new atomic macro is added. I was checking ALSA
> playback/capture and trigger() callback had to monitor some register
> status.
> 
> In general, the new macro can be used in atomic callbacks where regmap
> interface is used and polling is required.
> 

You should send a full patchset because it may turn out that the patch
which makes use of the new feature isn't correct or maybe the new
feature isn't really needed.

If there was a previous discussion about the need for this change, then
you should provide a link to that discussion.

Please note that usually changes without a real use-case in kernel are
not getting picked up or they are getting removed later on if nobody
makes use of them, so I assume this is a kind of an RFC patch for now.