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:   Tue, 10 Aug 2021 07:36:01 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-remoteproc <linux-remoteproc@...r.kernel.org>,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ohad Ben-Cohen <ohad@...ery.com>
Subject: Re: [PATCH v3 2/2] remoteproc: meson-mx-ao-arc: Add a driver for the
 AO ARC remote procesor

On Sun, 8 Aug 2021 at 14:37, Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:
>
> Hi Mathieu,
>
> On Thu, Aug 5, 2021 at 6:15 PM Mathieu Poirier
> <mathieu.poirier@...aro.org> 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.
> AO_CPU_CNTL_AHB_SRAM_BITS_31_20 is used below and when looking at it
> now I think the alignment is also strange.
> For the next version I'll go with the tmp variable as I think it
> improves readability, even with the long(er) macro names.
>
> [...]
> > > > > +     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().
> I could not find where __reset_control_get_from_lookup returns NULL in
> case optional is false (which it is in this case because
> devm_reset_control_get_exclusive requests a "mandatory" reset line).
> Can you please point me to the problematic line(s) as I'd like to send
> a patch (which fixes this) to the reset subsystem maintainers
>

I am currently traveling - I will get back to you in a week or so.

> $ git grep -A1 devm_reset_control_get_exclusive | grep IS_ERR_OR_NULL
> drivers/remoteproc/ti_k3_r5_remoteproc.c-       if
> (IS_ERR_OR_NULL(core->reset)) {
> $
>
> I suspect that this can be simplified then as well.
>
>
> Best regards,
> Martin
>
>
> [0] https://elixir.bootlin.com/linux/v5.14-rc4/source/include/linux/reset.h#L227
> [1] https://elixir.bootlin.com/linux/v5.14-rc4/source/drivers/reset/core.c#L932