linux-kernel - Re: [PATCH] Fix IXP4xx coherent allocations

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Message-ID: <1364863243.3557.136.camel@deadeye.wl.decadent.org.uk>
Date:	Tue, 2 Apr 2013 01:40:43 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Krzysztof Halasa <khc@...waw.pl>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	<linux-arm-kernel@...ts.infradead.org>, <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	<linux-kernel@...r.kernel.org>, <c.aeschlimann@...-group.ch>
Subject: Re: [PATCH] Fix IXP4xx coherent allocations

On Mon, 2013-04-01 at 22:17 +0200, Krzysztof Halasa wrote:
> Russell King - ARM Linux <linux@....linux.org.uk> writes:
> 
> > Right, so, the answer is - yes you are talking about platform devices,
> > and the reason that these aren't already set is because if you grep for
> > ixp4xx_eth or ixp4xx_hss in arch/arm/mach-ixp4xx, you'll notice that
> > _none_ of the device declarations set either of the DMA masks at all.
> > They don't even set the dev->dma_mask pointer.  That is why the masks
> > are zero.  For a device which does DMA, that is wrong.
> 
> Well, that's new to me. Please tell me how it should be done.
> Should I simply add in platform code (on all platforms):
> 
> +++ b/arch/arm/mach-ixp4xx/XXX.c
> @@ -380,10 +380,12 @@ static struct platform_device device_eth_tab[] = {
>          .name           = "ixp4xx_eth",
>          .id         = IXP4XX_ETH_NPEB,
>          .dev.platform_data  = eth_plat,
> +        .dev.coherent_dma_mask  = DMA_BIT_MASK(32),
>      }, {
>          .name           = "ixp4xx_eth",
>          .id         = IXP4XX_ETH_NPEC,
>          .dev.platform_data  = eth_plat + 1,
> +        .dev.coherent_dma_mask  = DMA_BIT_MASK(32),
>      }
>  };
> 
> This alone isn't going to work, the problem is coherent DMA mask in
> net_dev->dev and not in platform_device. So what do I do in the network
> drivers? Copy the masks from platform_device to the actual newly created
> net_dev->dev?
>
> Should I use the parent device (net_dev->dev.parent which is the
> platform_device) as the argument to the allocator? This would probably
> work though I'm not sure of its correctness.
[...]

Passing the parent device to DMA API functions seems to be the right
thing to do.  It's what you would do in a PCI device driver.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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