From: Terje Bergstrom <tbergstrom@nvidia.com>
To: Thierry Reding <thierry.reding@gmail.com>,
Alexandre Courbot <acourbot@nvidia.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>,
<dri-devel@lists.freedesktop.org>, <linux-tegra@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <gnurou@gmail.com>
Subject: Re: [PATCH 2/2] drm/tegra: Set the DMA mask
Date: Tue, 23 Feb 2016 08:18:26 -0800 [thread overview]
Message-ID: <56CC8652.8020208@nvidia.com> (raw)
In-Reply-To: <20160223160440.GE27656@ulmo>
On 02/23/2016 08:04 AM, Thierry Reding wrote:
> * PGP Signed by an unknown key > > On Tue, Feb 23, 2016 at 03:25:54PM +0900, Alexandre Courbot wrote:
>> The default DMA mask covers a 32 bits address range, but tegradrm >>
can address more than that. Set the DMA mask to the actual >>
addressable range to avoid the use of unneeded bounce buffers. >> >>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> --- Thierry, >> I
am not absolutely sure whether the size is correct and applies to >> all
Tegra generations - please let me know if this needs to be >> reworked.
>> >> drivers/gpu/drm/tegra/drm.c | 1 + 1 file changed, 1 insertion(+)
> > This kind of depends on whether or not the device is behind an
IOMMU. > If it is, then the IOMMU DMA MASK would apply, which can be
derived > from the number of address bits that the IOMMU can handle. The
SMMU > supports 32 address bits on Tegra30 and Tegra114, 34 address bits
on > more recent generations. > > I think for now it's safer to leave
the DMA mask at the default (32 > bit) to avoid the need to distinguish
between IOMMU and non-IOMMU > devices.
The GPUs after Tegra114 can choose per access whether they're using IOMMU
or not. The interface is 34 bits wide, so the physical addresses can be
34 bits.
IOMMU addresses are limited by Tegra SMMU to 32-bit for gk20a. gm20b can use
34-bit if SMMU is configured to combine four ASIDs together.
next prev parent reply other threads:[~2016-02-23 16:18 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 6:25 [PATCH 1/2] drm/tegra: Set DMA ops Alexandre Courbot
2016-02-23 6:25 ` [PATCH 2/2] drm/tegra: Set the DMA mask Alexandre Courbot
2016-02-23 16:04 ` Thierry Reding
2016-02-23 16:18 ` Terje Bergstrom [this message]
2016-02-23 16:27 ` Thierry Reding
2016-02-24 8:38 ` Alexandre Courbot
2016-02-23 15:28 ` [PATCH 1/2] drm/tegra: Set DMA ops Thierry Reding
2016-02-24 8:30 ` Alexandre Courbot
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