linux-kernel - Re: [PATCH v5 3/3] mmc: Add driver for LiteX's LiteSDCard interface

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Date:   Sun, 26 Dec 2021 15:13:21 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Gabriel L. Somlo" <gsomlo@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Karol Gugala <kgugala@...micro.com>,
        Mateusz Holenko <mholenko@...micro.com>, krakoczy@...micro.com,
        mdudek@...ernships.antmicro.com, paulus@...abs.org,
        Joel Stanley <joel@....id.au>,
        Stafford Horne <shorne@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        david.abdurachmanov@...ive.com, florent@...oy-digital.fr,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v5 3/3] mmc: Add driver for LiteX's LiteSDCard interface

On Sun, Dec 26, 2021 at 1:45 PM Gabriel L. Somlo <gsomlo@...il.com> wrote:
> On Sat, Dec 25, 2021 at 06:43:22PM +0200, Andy Shevchenko wrote:
> > On Wed, Dec 15, 2021 at 10:00 PM Gabriel Somlo <gsomlo@...il.com> wrote:

...

> > This is wrong. It missed the deferred probe, for example.
> >
> > The best approach is
> >
> > ret = platform_get_irq_optional(...);
> > if (ret < 0 && ret != -ENXIO)
> >   return ret;
> > if (ret > 0)
> >   ...we got it...
> >
> > It will allow the future API fix of platform_get_irq_optional() to be
> > really optional.
>
> Thanks for the example. I still need to work in a decision to use
> polling, though. How about something like this instead:
>
> ret = platform_get_irq_optional(...);
> if (ret == -ENXIO)
>   goto use_polling;
> if (ret < 0)
>   return ret; // deferred probe (-EAGAIN likely?)
> if (ret > 0)
>   ...we got it, keep going...

This doesn't define what you should do when you get 0.
I suggest to take my variant with below modification

if (ret > 0)
  ...we have IRQ...
else
  goto USE POLLING;

It will take care of the case.

...

> > > +#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
> >
> > Why under ifdeffery?
>
> Because I only want to do it on 64-bit capable architectures.
>
> The alternative would be to call
>
>   dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
>
> on *all* architectures, but ignore the returned error (-EIO,
> presumably on architetures that only support 32-bit DMA).

I don't understand why you are supposed to ignore errors and why you
expect to get such.

> Do you think that would be cleaner?

-- 
With Best Regards,
Andy Shevchenko