netdev - Re: [PATCH net] macmace: Set platform device coherent_dma

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Date:   Fri, 4 May 2018 09:24:02 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Michael Schmitz <schmitzmic@...il.com>
Cc:     Christoph Hellwig <hch@....de>,
        Finn Thain <fthain@...egraphics.com.au>,
        "David S. Miller" <davem@...emloft.net>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] macmace: Set platform device coherent_dma_mask

Hi Michael,

On Thu, May 3, 2018 at 10:24 PM, Michael Schmitz <schmitzmic@...il.com> wrote:
> On Thu, May 3, 2018 at 8:51 PM, Christoph Hellwig <hch@....de> wrote:
>> On Thu, May 03, 2018 at 10:46:56AM +0200, Geert Uytterhoeven wrote:
>>> Perhaps you can add a new helper (platform_device_register_simple_dma()?)
>>> that takes the DMA mask, too?
>>> With people setting the mask to kill the WARNING splat, this may become
>>> more common.
>>>
>>> struct platform_device_info already has a dma_mask field, but
>>> platform_device_register_resndata() explicitly sets it to zero.
>>
>> Yes, that would be useful.  The other assumption could be that
>> platform devices always allow an all-0xff dma mask.
>
> That's not always true (Atari NCR5380 SCSI and floppy would use a 24
> bit DMA mask). We use bounce buffers allocated from a dedicated lowmem
> pool there currently, and for all I know don't use the DMA API yet.
>
> I bet that is a rare exception though. Setting the default DMA mask
> for platform devices to all-0xff and letting the few odd drivers force
> a different setting seems the best way forward.

I'd say that's usually a property of the platform, not of the device?
So IMHO it belongs in the platform code, not in the device driver code.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds