On 11/8/22 20:06, Robin Murphy wrote:
> Although we don't use 1GB block mappings, we still need to split
> map/unmap requests at 1GB boundaries to match what io-pgtable expects.
> Fix that, and add some explanation to make sense of it all.
>
> Fixes: 3740b081795a ("drm/panfrost: Update io-pgtable API")
> Reported-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
> Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> ---
> The previous diff turned out to be not quite right, so I've not
> included Dmitry's Tested-by given for that.
> ---
> drivers/gpu/drm/panfrost/panfrost_mmu.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> index e246d914e7f6..4e83a1891f3e 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
> @@ -250,13 +250,22 @@ void panfrost_mmu_reset(struct panfrost_device *pfdev)
>
> static size_t get_pgsize(u64 addr, size_t size, size_t *count)
> {
> + /*
> + * io-pgtable only operates on multiple pages within a single table
> + * entry, so we need to split at boundaries of the table size, i.e.
> + * the next block size up. The distance from address A to the next
> + * boundary of block size B is logically B - A % B, but in unsigned
> + * two's complement where B is a power of two we get the equivalence
> + * B - A % B == (B - A) % B == (n * B - A) % B, and choose n = 0 :)
> + */
> size_t blk_offset = -addr % SZ_2M;
>
> if (blk_offset || size < SZ_2M) {
> *count = min_not_zero(blk_offset, size) / SZ_4K;
> return SZ_4K;
> }
> - *count = size / SZ_2M;
> + blk_offset = -addr % SZ_1G ?: SZ_1G;
> + *count = min(blk_offset, size) / SZ_2M;
> return SZ_2M;
> }
>
This variant also works fine, thanks!
Tested-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
--
Best regards,
Dmitry
