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From: Michael Schmitz <schmitzmic@gmail.com>
To: Finn Thain <fthain@telegraphics.com.au>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	"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>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH net] macmace: Set platform device coherent_dma_mask
Date: Sat, 12 May 2018 10:02:03 +1200	[thread overview]
Message-ID: <23ed7ff8-c1d7-a069-3058-3944c7586116@gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.21.1805112003250.8@nippy.intranet>

Hi Finn,

Am 11.05.2018 um 22:06 schrieb Finn Thain:
>> You would have to be careful not to overwrite a pdev->dev.dma_mask and 
>> pdev->dev.dma_coherent_mask that might have been set in a platform 
>> device passed via platform_device_register here. Coldfire is the only 
>> m68k platform currently using that, but there might be others in future.
>>
> 
> That Coldfire patch could be reverted if this is a better solution.

True, but there might be other uses for deviating from a platform
default (I'm thinking of Atari SCSI and floppy drivers here). But we
could chose the correct mask to set in arch_setup_pdev_archdata()
instead, as it's a platform property not a driver property in that case.

>> ... But I don't think there are smaller DMA masks used by m68k drivers 
>> that use the platform device mechanism at present. I've only looked at 
>> arch/m68k though.
> 
> So we're back at the same problem that Geert's suggestion also raised: how 
> to identify potentially affected platform devices and drivers?
> 
> Maybe we can take a leaf out of Christoph's book, and leave a noisy 
> WARNING splat in the log.
> 
> void arch_setup_pdev_archdata(struct platform_device *pdev)
> {
>         WARN_ON_ONCE(pdev->dev.coherent_dma_mask != DMA_MASK_NONE ||
>                      pdev->dev.dma_mask != NULL);

I'd suggest using WARN_ON() so we catch all uses on a particular platform.

I initially thought it necessary to warn on unset mask here, but I see
that would throw up a lot of redundant false positives.

Cheers,

	Michael

  reply	other threads:[~2018-05-11 22:02 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
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 [this message]
2018-05-03  4:23 Finn Thain

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