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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Date:   Mon, 23 Aug 2021 09:29:30 -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 Thu, Aug 05, 2021 at 10:15:06AM -0600, Mathieu Poirier wrote:
> 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().
> 

You are correct, in your case checking for IS_ERR() is sufficient.

> > 
> > 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