linux-kernel - Re: [PATCH v3 2/2] remoteproc: meson-mx-ao-arc: Add a driver for the AO ARC remote procesor

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Message-ID: <20210805161506.GA3205691@p14s>
Date:   Thu, 5 Aug 2021 10:15:06 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-remoteproc@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bjorn.andersson@...aro.org, ohad@...ery.com
Subject: Re: [PATCH v3 2/2] remoteproc: meson-mx-ao-arc: Add a driver for the
 AO ARC remote procesor

On Wed, Aug 04, 2021 at 11:03:57PM +0200, Martin Blumenstingl wrote:
> Hi Mathieu,
> 
> thanks for taking the time to look into this!
> 
> (I will address any of your comments that I am not mentioning in this
> email anymore. Thanks a lot for the suggestions!)
> 
> On Wed, Jul 28, 2021 at 7:58 PM Mathieu Poirier
> <mathieu.poirier@...aro.org> wrote:
> [...]
> > > +     writel(FIELD_PREP(AO_REMAP_REG0_REMAP_AHB_SRAM_BITS_17_14_FOR_ARM_CPU,
> > > +                            priv->sram_pa >> 14),
> > Indentation problem
> The idea here is to align priv->sram_pa with AO_REMAP_REG0... which
> are both arguments to FIELD_PREP

Right, this is what I would have expected.  When I applied the patch on my side
"priv->sram_pa ..." was aligned wiht the 'M' of "AO_REMAP_ ...".  

> Maybe using something like this will make that easier to read:
>     tmp = FIELD_PREP(AO_REMAP_REG0_REMAP_AHB_SRAM_BITS_17_14_FOR_ARM_CPU,
>                                      priv->sram_pa >> 14);
>     writel(tmp, priv->remap_base + AO_REMAP_REG0);

I think the main problem is that
AO_REMAP_REG0_REMAP_AHB_SRAM_BITS_17_14_FOR_ARM_CPU is simply too long.  I
suggest making is shorter and add a comment to describe exactly what it does.

> 
> What do you think: leave it as is or use a separate variable?
> 
> [...]
> > > +     usleep_range(10, 100);
> >
> > I've seen this kind of mysterious timeouts in other patchset based vendor trees.
> > You likely don't know why it is needed so I won't ask.
> unfortunately this is also the case here
> 
> [...]
> > > +     priv->arc_reset = devm_reset_control_get_exclusive(dev, NULL);
> > > +     if (IS_ERR(priv->arc_reset)) {
> >
> > Function __reset_control_get() in __devm_reset_control_get() can return NULL so
> > this should be IS_ERR_OR_NULL().
> The logic in there is: return optional ? NULL : ERR_PTR(-...);

Ok, so you meant to do that.  And I just checked reset_control_reset() and it does
account for a NULL parameter.  I'm good with this one but add a comment to
make sure future readers don't think you've omitted to properly deal with the
NULL return value.

> I am requesting a mandatory reset line here, so reset core will never
> return NULL
> See also [0]

Indeed, I've read that too.  Nonetheless __reset_control_get() can return NULL
by way of __reset_control_get_from_lookup().

> 
> For this reason I am not planning to change this
> 
> [...]
> > This driver is squeaky clean. With the above:
> >
> > Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> awesome, thank you!
> 
> 
> Best regards,
> Martin
> 
> 
> [0] https://elixir.bootlin.com/linux/v5.14-rc4/source/include/linux/reset.h#L227