linux-kernel - Re: [PATCH] regmap: don't check for alignment when using reg

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Message-ID: <bb836be3-456c-48fd-9b19-62279fee6b8d@sirena.org.uk>
Date:   Tue, 25 Apr 2023 13:56:23 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Colin Foster <colin.foster@...advantage.com>
Cc:     Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org,
        thomas.petazzoni@...tlin.com, alexis.lothore@...tlin.com
Subject: Re: [PATCH] regmap: don't check for alignment when using reg_shift

On Fri, Apr 21, 2023 at 08:50:30AM -0700, Colin Foster wrote:
> On Thu, Apr 20, 2023 at 05:06:17PM +0200, Maxime Chevallier wrote:

> > On regmap consumers that require address translation through
> > up/downshifting, the alignment check in the regmap core doesn't take the
> > translation into account. This doesn't matter when downshifting the
> > register address, as any address that fits a given alignment requirement
> > will still meet it when downshifted (a 4-byte aligned address will
> > always also be 2-bytes aligned for example).

> > However, when upshifting, this check causes spurious errors, as it
> > occurs before the upshifting.

> I don't follow why upshifting should make a difference to alignment.
> Assuming it does though, would it make sense to test

> map->format.reg_shift > 0

> instead of just !map->format.reg_shift?

Yeah, I think the question is more when we should run the alignment
check than if we should have one.  I think running the check after any
shifting makes sense, we'd be better off reorganising the checks if
needed than removing them.

> 
> > -	if (!IS_ALIGNED(reg, map->reg_stride))
> > +	if (!map->format.reg_shift && !IS_ALIGNED(reg, map->reg_stride))
> >  		return -EINVAL;
> 
> In the case of ocelot_spi, we'd want to flag an invalid access to a
> register like 0x71070003... Before this patch it would return -EINVAL,
> after this patch it would access 0x71070000.
> 
> Colin Foster

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