linux-kernel - Re: using DMA-API on ARM

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Message-ID: <5486D7EF.6010902@broadcom.com>
Date:	Tue, 9 Dec 2014 12:07:27 +0100
From:	Arend van Spriel <arend@...adcom.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Catalin Marinas <catalin.marinas@....com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	brcm80211-dev-list <brcm80211-dev-list@...adcom.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	"Hante Meuleman" <meuleman@...adcom.com>,
	"hauke@...ke-m.de" <hauke@...ke-m.de>,
	David Miller <davem@...emloft.net>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: using DMA-API on ARM

On 12/09/14 11:29, Russell King - ARM Linux wrote:
> On Tue, Dec 09, 2014 at 11:19:40AM +0100, Arend van Spriel wrote:
>> The issue did not trigger overnight so it seems setting bit 22<Shared
>> Attribute _Override_ Enable>  solves the issue over here. Now the question is
>> how to move forward with this. As I understood from Catalin this patch was
>> not included as it was not considered responsibility of the linux kernel.
>
> It is preferable for firmware to configure the L2 cache appropriately,
> which includes things like the prefetch offsets as well as feature bits
> like bit 22.
>
> I think what I'll do is queue up a patch which adds a warning if bit 22
> is not set, suggesting that firmware is updated to set this bit.

I was thinking in the same direction. Thanks to you all for looking into 
this. It did not feel right to use the dma_sync_single_for_cpu() for 
memory allocated with dma_alloc_coherent() and I am glad this got 
cleared up.

Regards,
Arend

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