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

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Date:   Sun, 26 Dec 2021 08:36:47 -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

On Sun, Dec 26, 2021 at 03:13:21PM +0200, Andy Shevchenko wrote:
> 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.
 
OK, will do.

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

If I call `dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));`
on a machine where `CONFIG_ARCH_DMA_ADDR_T_64BIT` is *not* set, I
expect an error. The implicit default
(per Documentation/core-api/dma-api-howto.rst), is DMA_BIT_MASK(32).
I'm working under the impression that on machines with
CONFIG_ARCH_DMA_ADDR_T_64BIT I should increase that to DMA_BIT_MASK(64).

So if I don't #ifdef it, that call will fail on machines supporting
only 32-bits.

What am I missing?

Thanks,
--Gabriel
 
> > Do you think that would be cleaner?
> 
> -- 
> With Best Regards,
> Andy Shevchenko