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

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Message-ID: <b14d6130-8a9e-28ac-3ce6-dc6b9e3a3886@nvidia.com>
Date:   Fri, 10 Jan 2020 10:20:05 +0530
From:   Sameer Pujar <spujar@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


On 1/9/2020 7:27 PM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 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.

OK. I will send this as part of the complete series. Thank you.