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From: Michael Schmitz <schmitzmic@gmail.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Finn Thain <fthain@telegraphics.com.au>,
	"David S. Miller" <davem@davemloft.net>,
	linux-m68k <linux-m68k@vger.kernel.org>,
	netdev <netdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net] macmace: Set platform device coherent_dma_mask
Date: Fri, 4 May 2018 08:24:38 +1200	[thread overview]
Message-ID: <CAOmrzk+y5pmm2anaw15pch--y_gqoUO4NQemSbSanAXpEnttkg@mail.gmail.com> (raw)
In-Reply-To: <20180503085120.GA14574@lst.de>

Hi Christoph,

On Thu, May 3, 2018 at 8:51 PM, Christoph Hellwig <hch@lst.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.

Cheers,

  Michael



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  reply	other threads:[~2018-05-03 20:24 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <S1751632AbeECEYA/20180503042400Z+254@vger.kernel.org>
2018-05-03  7:25 ` Geert Uytterhoeven
2018-05-03  8:38   ` Finn Thain
2018-05-03  8:46     ` Geert Uytterhoeven
2018-05-03  8:51       ` Christoph Hellwig
2018-05-03 20:24         ` Michael Schmitz [this message]
2018-05-04  7:24           ` Geert Uytterhoeven
2018-05-04  8:16             ` Michael Schmitz
2018-05-10  1:25         ` Finn Thain
2018-05-10  1:25       ` Finn Thain
2018-05-10 20:27         ` Michael Schmitz
2018-05-10 23:55           ` Finn Thain
2018-05-11  2:11             ` Michael Schmitz
2018-05-11  3:28               ` Finn Thain
2018-05-11  4:18                 ` Michael Schmitz
2018-05-11  5:28                   ` Finn Thain
2018-05-11  9:30                     ` Michael Schmitz
2018-05-11 10:06                       ` Finn Thain
2018-05-11 22:02                         ` Michael Schmitz
2018-05-03  4:23 Finn Thain

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