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

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Message-ID: <YchV5UvIq7xgkbF6@glsvmlin.ini.cmu.edu>
Date:   Sun, 26 Dec 2021 06:45:41 -0500
From:   "Gabriel L. Somlo" <gsomlo@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...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

Hi Andy,

Thanks for the feedback!

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:
> >
> > LiteX (https://github.com/enjoy-digital/litex) is a SoC framework
> > that targets FPGAs. LiteSDCard is a small footprint, configurable
> > SDCard core commonly used in LiteX designs.
> >
> > The driver was first written in May 2020 and has been maintained
> > cooperatively by the LiteX community. Thanks to all contributors!
> 
> ...
> 
> > +       int ret;
> > +
> > +       host->irq = platform_get_irq_optional(host->dev, 0);
> > +       if (host->irq <= 0) {
> > +               dev_warn(dev, "Failed to get IRQ, using polling\n");
> > +               goto use_polling;
> > +       }
> 
> [Same comment as per v3.]

> 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...

> 
> ...
> 
> > +#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).

Do you think that would be cleaner?

Thanks,
--Gabriel

> > +       /* increase from default 32 on 64-bit-DMA capable architectures */
> > +       ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
> > +       if (ret)
> > +               goto err;
> > +#endif
> 
> With Best Regards,
> Andy Shevchenko