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

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Message-ID: <20141209115425.GB31129@e104818-lin.cambridge.arm.com>
Date:	Tue, 9 Dec 2014 11:54:26 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Arend van Spriel <arend@...adcom.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 Tue, Dec 09, 2014 at 10:29:05AM +0000, 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'm fine with a (big) warning on this bit. But when you boot in secure
mode on 32-bit, do we still have a read/modify/write sequence for
L2X0_AUX_CTRL? A quick look at l2c310_enable() didn't reveal this (the
code has changed since I proposed the bit 22 setting patch).

-- 
Catalin
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