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

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Date:   Sun, 26 Dec 2021 15:01:20 +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:
>
> 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



-- 
With Best Regards,
Andy Shevchenko