Re: [PATCH] drm/panfrost: Update io-pgtable API

[Robin Murphy]

On 2022-11-04 20:11, Dmitry Osipenko wrote:
On 8/23/22 01:01, Robin Murphy wrote:
Convert to io-pgtable's bulk {map,unmap}_pages() APIs, to help the old
single-page interfaces eventually go away. Unmapping heap BOs still
wants to be done a page at a time, but everything else can get the full
benefit of the more efficient interface.
Signed-off-by: Robin Murphy <robin.mur...@arm.com>
---
  drivers/gpu/drm/panfrost/panfrost_mmu.c | 40 +++++++++++++++----------
  1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c 
b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index b285a8001b1d..e246d914e7f6 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -248,11 +248,15 @@ void panfrost_mmu_reset(struct panfrost_device *pfdev)
        mmu_write(pfdev, MMU_INT_MASK, ~0);
  }
  
-static size_t get_pgsize(u64 addr, size_t size)
+static size_t get_pgsize(u64 addr, size_t size, size_t *count)
  {
-       if (addr & (SZ_2M - 1) || size < SZ_2M)
-               return SZ_4K;
+       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;
        return SZ_2M;
  }
  
@@ -287,12 +291,16 @@ static int mmu_map_sg(struct panfrost_device *pfdev, struct panfrost_mmu *mmu,
                dev_dbg(pfdev->dev, "map: as=%d, iova=%llx, paddr=%lx, len=%zx", 
mmu->as, iova, paddr, len);
  
  		while (len) {
-                       size_t pgsize = get_pgsize(iova | paddr, len);
+                       size_t pgcount, mapped = 0;
+                       size_t pgsize = get_pgsize(iova | paddr, len, &pgcount);
  
-			ops->map(ops, iova, paddr, pgsize, prot, GFP_KERNEL);
-                       iova += pgsize;
-                       paddr += pgsize;
-                       len -= pgsize;
+                       ops->map_pages(ops, iova, paddr, pgsize, pgcount, prot,
+                                      GFP_KERNEL, &mapped);
+                       /* Don't get stuck if things have gone wrong */
+                       mapped = max(mapped, pgsize);
+                       iova += mapped;
+                       paddr += mapped;
+                       len -= mapped;
                }
        }
  
@@ -344,15 +352,17 @@ void panfrost_mmu_unmap(struct panfrost_gem_mapping *mapping)
                mapping->mmu->as, iova, len);
  
  	while (unmapped_len < len) {
-               size_t unmapped_page;
-               size_t pgsize = get_pgsize(iova, len - unmapped_len);
+               size_t unmapped_page, pgcount;
+               size_t pgsize = get_pgsize(iova, len - unmapped_len, &pgcount);
  
-		if (ops->iova_to_phys(ops, iova)) {
-                       unmapped_page = ops->unmap(ops, iova, pgsize, NULL);
-                       WARN_ON(unmapped_page != pgsize);
+               if (bo->is_heap)
+                       pgcount = 1;
+               if (!bo->is_heap || ops->iova_to_phys(ops, iova)) {
+                       unmapped_page = ops->unmap_pages(ops, iova, pgsize, 
pgcount, NULL);
+                       WARN_ON(unmapped_page != pgsize * pgcount);

This patch causes this WARN_ON to trigger. It doesn't happen all the
time, I see that the whole unmapped area is mapped. Initially, I thought
that this happens because it tries to unmap a partially mapped range,
but I checked that ops->iova_to_phys() returns address for all 4k chunks.

For example the pgsize * pgcount = 0x8000000, while returned
unmapped_page = 0x6000000.

I don't see this problem with this patch reverted. This is using today's
linux-next. Any ideas?

What's the base IOVA in such a case? I'm wondering if the truncated size 
lines up to any interesting boundary. Presumably you're not seeing any 
additional warnings from io-pgtable itself?

Thanks,
Robin.