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From: Finn Thain <fthain@telegraphics.com.au>
To: Michael Schmitz <schmitzmic@gmail.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "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: Fri, 11 May 2018 15:28:58 +1000 (AEST)	[thread overview]
Message-ID: <alpine.LNX.2.21.1805111451220.8@nippy.intranet> (raw)
In-Reply-To: <0b13a08d-ba2d-b9dc-4fd9-1f6bad5cd1ee@gmail.com>

On Fri, 11 May 2018, Michael Schmitz wrote:

> 
> I'm afraid using platform_device_register() (which you already use for 
> the SCC devices) is the only option handling this on a per-device basis 
> without touching platform core code, while at the same time keeping the 
> DMA mask setup out of device drivers

I don't think that will fly. If you call platform_device_register() and 
follow that with a dma mask assignment, you could race with the bus 
matching and driver probe, and we are back to the same WARNING message.

If you want to use platform_device_register(), you'd have to implement 
arch_setup_pdev_archdata() and use that to set up the dma mask.

> (I can see Geert's point there - device driver code might be shared 
> across implementations of the device on platforms with different DMA 
> mask requirements,, something the driver can't be expected to know 
> about).

As I said, these drivers might be expected to be portable between Macs and 
early PowerMacs, but the same dma mask would apply AFAIK.

If a platform driver isn't expected to be portable, I think either method 
is reasonable: arch_setup_pdev_archdata() or the method in the patch.

Anyway, there is this in arch/powerpc/kernel/setup-common.c:

void arch_setup_pdev_archdata(struct platform_device *pdev)
{
        pdev->archdata.dma_mask = DMA_BIT_MASK(32);
        pdev->dev.dma_mask = &pdev->archdata.dma_mask;
	...

I'm inclined to propose something similar for m68k. That should fix the 
problem, since arch_setup_pdev_archdata() is already in the call chain:

	platform_device_register_simple()
		platform_device_register_resndata()
			platform_device_register_full()
				platform_device_alloc()
					arch_setup_pdev_archdata()

Thoughts? Will this have nasty side effects for m68k platforms that use 
smaller dma masks?

-- 

> 
> Cheers,
> 
> 	Michael
> 

  reply	other threads:[~2018-05-11  5:29 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 [this message]
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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