Re: [PATCH] drm/mm: Support 4 GiB and larger ranges

[Thierry Reding <thierry.reding@gmail.com>]

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On Tue, Jan 27, 2015 at 07:07:44AM +0100, Thomas Hellstrom wrote:
> On 01/26/2015 11:51 PM, Dave Airlie wrote:
> > On 23 January 2015 at 18:05, Thierry Reding <thierry.reding@gmail.com> wrote:
> >> From: Thierry Reding <treding@nvidia.com>
> >>
> >> The current implementation is limited by the number of addresses that
> >> fit into an unsigned long. This causes problems on 32-bit Tegra where
> >> unsigned long is 32-bit but drm_mm is used to manage an IOVA space of
> >> 4 GiB. Given the 32-bit limitation, the range is limited to 4 GiB - 1
> >> (or 4 GiB - 4 KiB for page granularity).
> >>
> >> This commit changes the start and size of the range to be an unsigned
> >> 64-bit integer, thus allowing much larger ranges to be supported.
> > This seems fine to me, Chris, Daniel or Thomas, any objections?
> >
> > Dave.
> 
> This is perfectly fine with me, although I'm a bit curious why the
> allocation granularity of the IOVA space needs to be 1 byte?

Are you referring to the 4 GiB - 1 comment? The point I was trying to
make is not that the granularity of the IOVA space needs to be 1 byte
but rather that using an unsigned long for a size on a 32-bit machine
will give you 4 GiB - 1 addresses. The IOMMU page size is still 4 KiB
for Tegra.

Thierry

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