linux-kernel - Re: [PATCH v7 14/33] crypto: rockchip: handle reset also in PM

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Message-ID: <YrHJn6Pl5B/1pj9L@donbot>
Date:   Tue, 21 Jun 2022 14:37:35 +0100
From:   John Keeping <john@...anate.com>
To:     LABBE Corentin <clabbe@...libre.com>
Cc:     heiko@...ech.de, ardb@...nel.org, herbert@...dor.apana.org.au,
        krzysztof.kozlowski+dt@...aro.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v7 14/33] crypto: rockchip: handle reset also in PM

On Tue, Jun 21, 2022 at 10:05:54AM +0200, LABBE Corentin wrote:
> Le Mon, Jun 20, 2022 at 12:04:24PM +0100, John Keeping a écrit :
> > On Sun, May 08, 2022 at 06:59:38PM +0000, Corentin Labbe wrote:
> > > reset could be handled by PM functions.
> > 
> > Is there any further rationale for this?
> > 
> > After this change there is no longer a guaranteed reset pulse on probe
> > since the reset control may already be de-asserted.  This is normally
> > the most important case for a reset as it's the only time when the state
> > of the hardware is unknown.
> > 
> > The original use of devm_add_action_or_reset() seems a bit weird already
> > since there doesn't seem to be any need to assert reset when the driver
> > is unloaded.
> > 
> 
> I am not an hw engineer, so my knowledge on reset is low.
> So why not having a reset pulse on probe is a problem ?

The point of the reset is to bring the hardware back to a known state.
Since we don't know what state the hardware will be in following the
bootloader or previous OS, I think the reset in probe is the only place
that it is important.

If this patch isn't fixing anything, I suggest just dropping it.