linux-kernel - Re: [PATCH] spi: add runtime PM for transfer_one

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Message-ID: <20201102181655.GC5014@sirena.org.uk>
Date:   Mon, 2 Nov 2020 18:16:55 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Chunyan Zhang <zhang.lyra@...il.com>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang7@...il.com>,
        Chunyan Zhang <chunyan.zhang@...soc.com>,
        Bangzheng Liu <bangzheng.liu@...soc.com>
Subject: Re: [PATCH] spi: add runtime PM for transfer_one_message

On Mon, Nov 02, 2020 at 07:22:39PM +0800, Chunyan Zhang wrote:
> From: Chunyan Zhang <chunyan.zhang@...soc.com>

> Before transfer message, spi devices probably have been in runtime suspended,
> that would cause the kernel crash on some platforms once access spi
> registers, such as on Unisoc's SoCs. The spi devices can be suspended
> until message transfer completed.

This commit message is a bit hard to follow so I don't really understand
what the issue is.  We only ever call transfer_one_message() from within
__spi_pump_messages() which already handles auto_runtime_pm so I'm not
seeing the situation where we might get to transfer_one_message()
without having already runtime resumed the controller.  What exactly is
the error situation here?  This code has been around for a while and I'm
not aware of reports of issues here and I can't see anything unusual
that the Spreadtrum driver is doing.

Also why are we doing this in transfer_one_message() where it will only
work for controllers using that?  If we're missing runtime PM in some
paths then presumably controllers with a custom implementation are also
going to be affected as well, auto_runtime_pm is supposed to work for
them as well.

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