linux-kernel - Re: [PATCH v4 1/3] videobuf2-dma-contig: user can specify GFP flags

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Message-id: <50EBF7A9.6070802@samsung.com>
Date:	Tue, 08 Jan 2013 11:40:41 +0100
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Federico Vaga <federico.vaga@...il.com>
Cc:	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Pawel Osciak <pawel@...iak.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Giancarlo Asnaghi <giancarlo.asnaghi@...com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v4 1/3] videobuf2-dma-contig: user can specify GFP flags

Hello,

On 1/8/2013 11:15 AM, Federico Vaga wrote:
> > > @@ -165,7 +161,8 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned
> > > long size)>
> > >   	/* align image size to PAGE_SIZE */
> > >   	size = PAGE_ALIGN(size);
> > >
> > > -	buf->vaddr = dma_alloc_coherent(dev, size, &buf->dma_addr,
> GFP_KERNEL);
> > > +	buf->vaddr = dma_alloc_coherent(dev, size, &buf->dma_addr,
> > > +									
> GFP_KERNEL | conf->mem_flags);
> >
> > I think we can add GFP_DMA flag unconditionally to the vb2_dc_contig
> > allocator.
> > It won't hurt existing clients as most of nowadays platforms doesn't
> > have DMA
> > zone (GFP_DMA is ignored in such case), but it should fix the issues
> > with some
> > older and non-standard systems.
>
> I did not set GFP_DMA fixed in the allocator because I do not want to brake
> something in the future. On x86 platform GFP_DMA allocates under 16MB and this
> limit can be too strict. When many other drivers use GFP_DMA we can saturate
> this tiny zone.
> As you said, this fix the issue with _older_ and _non-standard_ (like sta2x11)
> systems. But this fix has effect on every other standard and new systems.
> That's why I preferred to set the flag optionally.

Ok, then I would simply pass the flags from the driver without any 
alternation
in the allocator itself, so drivers can pass 'GFP_KERNEL' or
'GFP_KERNEL | GFP_DMA' depending on their preference. Please also update 
all
the existing clients of vb2_dma_dc allocator.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center


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