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From: Lucas Stach <l.stach@pengutronix.de>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: kernel@pengutronix.de, etnaviv@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/etnaviv: select CMA and DMA_CMA if available
Date: Mon, 17 Jul 2017 10:49:53 +0200	[thread overview]
Message-ID: <1500281393.6594.24.camel@pengutronix.de> (raw)
In-Reply-To: <20170716152943.GH31807@n2100.armlinux.org.uk>

Am Sonntag, den 16.07.2017, 16:29 +0100 schrieb Russell King - ARM
Linux:
> On Fri, Jul 14, 2017 at 04:38:01PM +0200, Lucas Stach wrote:
> > While this is no build dependency, etnaviv will only work correctly on most
> > systems if CMA and DMA_CMA are enabled. Select both options if available to
> > avoid users ending up with a non-working GPU due to a lacking kernel config.
> 
> How does merely selecting CMA solve this problem?  Does CMA guarantee
> that GPU command buffers will always be allocated in the lower 2G of
> physical address space?

No, but CMA guarantees that commandbuffers will be allocated from the
region and with the default CMA configuration dma_get_required_mask()
will return the correct location of the CMA area, so we can move the
linear memory window accordingly.
There are no guarantees, but at least with a CMA area no larger than 2GB
things will work for the average user, which is a lot better than
leaving them with a non-working GPU due to a simple missing kernel
configuration option.

Regards,
Lucas

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      reply	other threads:[~2017-07-17  8:49 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-14 14:38 [PATCH] drm/etnaviv: select CMA and DMA_CMA if available Lucas Stach
2017-07-14 18:32 ` Joshua Clayton
2017-07-17  8:52   ` Lucas Stach
2017-07-16 15:29 ` Russell King - ARM Linux
2017-07-17  8:49   ` Lucas Stach [this message]

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