RE: [PATCH] lib/intel_pat: Handle platforms without compressed PAT index

Gurram, Pravalika
2026-03-03T11:32:37Z

> -----Original Message-----
> From: Yadav, Sanjay Kumar <sanjay.kumar.yadav@intel.com>
> Sent: Tuesday, 3 March, 2026 04:01 PM
> To: Gurram, Pravalika <pravalika.gurram@intel.com>; igt-
> dev@lists.freedesktop.org
> Cc: Auld, Matthew <matthew.auld@intel.com>
> Subject: Re: [PATCH] lib/intel_pat: Handle platforms without compressed PAT
> index
>
>
> On 03-03-2026 15:20, Gurram, Pravalika wrote:
> >
> >> -----Original Message-----
> >> From: igt-dev <igt-dev-bounces@lists.freedesktop.org> On Behalf Of
> >> Sanjay Yadav
> >> Sent: Wednesday, 18 February, 2026 04:06 PM
> >> To: igt-dev@lists.freedesktop.org
> >> Cc: Auld, Matthew <matthew.auld@intel.com>
> >> Subject: [PATCH] lib/intel_pat: Handle platforms without compressed
> >> PAT index
> >>
> >> Previously intel_get_pat_idx_uc_comp() would silently return zero on
> >> platforms where no compressed PAT index exists (e.g. CRI), since
> >> uc_comp was zero-initialized by default. This could lead to incorrect
> >> behavior when callers assume the returned index is valid.
> >>
> >> Fix this by:
> >> - Adding XE_PAT_IDX_INVALID sentinel to detect unsupported platforms
> >> - Initializing uc_comp to XE_PAT_IDX_INVALID in intel_get_pat_idx();
> >> only platforms with CCS (graphics_ver 20/30) override it to a valid
> >> index
> >> - Adding igt_assert_f() in intel_get_pat_idx_uc_comp() to fail with
> >> a clear error instead of returning an invalid index
> >>
> >> Also update the bo-comp-disable-bind test to distinguish between "CCS
> >> is disabled" and "CCS does not exist" using HAS_FLATCCS(). On
> >> platforms without CCS, the compressed PAT bind check is skipped since
> >> there is no valid compressed PAT index to test with.
> >>
> >> Suggested-by: Matthew Auld <matthew.auld@intel.com>
> >> Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
> >> ---
> >> lib/intel_pat.c | 5 +++++
> >> lib/intel_pat.h | 1 +
> >> tests/intel/xe_pat.c | 30 ++++++++++++++++++++++--------
> >> 3 files changed, 28 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/lib/intel_pat.c b/lib/intel_pat.c index
> >> 9815efc18..d30bee453
> >> 100644
> >> --- a/lib/intel_pat.c
> >> +++ b/lib/intel_pat.c
> >> @@ -98,6 +98,8 @@ static void intel_get_pat_idx(int fd, struct
> >> intel_pat_cache *pat) {
> >> uint16_t dev_id = intel_get_drm_devid(fd);
> >>
> >> + pat->uc_comp = XE_PAT_IDX_INVALID;
> >> +
> >> if (intel_graphics_ver(dev_id) == IP_VER(35, 11)) {
> >> pat->uc = 3;
> >> pat->wb = 2;
> >> @@ -155,8 +157,11 @@ uint8_t intel_get_pat_idx_uc_comp(int fd)
> >> uint16_t dev_id = intel_get_drm_devid(fd);
> >>
> >> igt_assert(intel_gen(dev_id) >= 20);
> >> + igt_assert(HAS_FLATCCS(dev_id));
> >>
> >> intel_get_pat_idx(fd, &pat);
> >> + igt_assert_f(pat.uc_comp != XE_PAT_IDX_INVALID,
> >> + "No compressed PAT index available on this platform\n");
> >> return pat.uc_comp;
> >> }
> >>
> >> diff --git a/lib/intel_pat.h b/lib/intel_pat.h index
> >> e9ade2e2e..e5dd8a0af
> >> 100644
> >> --- a/lib/intel_pat.h
> >> +++ b/lib/intel_pat.h
> >> @@ -10,6 +10,7 @@
> >> #include <stdint.h>
> >>
> >> #define DEFAULT_PAT_INDEX ((uint8_t)-1) /* igt-core can pick 1way
> >> or better */
> >> +#define XE_PAT_IDX_INVALID ((uint8_t)-2) /* no such PAT index on
> >> +this platform */
> >> #define XE_PAT_MAX_ENTRIES 32
> >>
> >> struct xe_pat_entry {
> >> diff --git a/tests/intel/xe_pat.c b/tests/intel/xe_pat.c index
> >> 21547c84e..052b7b699 100644
> >> --- a/tests/intel/xe_pat.c
> >> +++ b/tests/intel/xe_pat.c
> >> @@ -844,15 +844,18 @@ static bool has_no_compression_hint(int fd)
> >> * Test category: functionality test
> >> * Description: Validates that binding a BO created with
> >> * the NO_COMPRESSION flag using a compressed PAT index fails
> >> - * with -EINVAL on Xe2+ platforms.
> >> + * with -EINVAL on Xe2+ platforms. On platforms where CCS
> >> + * does not exist, the test verifies uncompressed access works.
> >> */
> >>
> >> static void bo_comp_disable_bind(int fd) {
> >> size_t size = xe_get_default_alignment(fd);
> >> - uint8_t comp_pat_index, uncomp_pat_index;
> >> - bool supported;
> >> + uint16_t dev_id = intel_get_drm_devid(fd);
> >> + bool has_flatccs = HAS_FLATCCS(dev_id);
> >> + uint8_t uncomp_pat_index;
> >> uint32_t vm, bo;
> >> + bool supported;
> >> int ret;
> >>
> >> supported = has_no_compression_hint(fd); @@ -868,14 +871,25
> @@
> >> static void bo_comp_disable_bind(int fd)
> >> igt_assert_eq(ret, 0);
> >> vm = xe_vm_create(fd, 0, 0);
> >>
> >> - comp_pat_index = intel_get_pat_idx_uc_comp(fd);
> >> uncomp_pat_index = intel_get_pat_idx_uc(fd);
> >>
> >> - igt_assert_eq(__xe_vm_bind(fd, vm, 0, bo, 0, 0x100000,
> >> - size, 0, 0, NULL, 0,
> >> - 0, comp_pat_index, 0),
> >> - -EINVAL);
> >> + /*
> >> + * On platforms with CCS, binding a NO_COMPRESSION BO with a
> >> + * compressed PAT index must fail. On platforms without CCS,
> >> + * there is no valid compressed PAT index, so skip this check.
> >> + */
> >> + if (has_flatccs) {
> >> + uint8_t comp_pat_index = intel_get_pat_idx_uc_comp(fd);
> >> +
> >> + igt_assert_eq(__xe_vm_bind(fd, vm, 0, bo, 0, 0x100000,
> >> + size, 0, 0, NULL, 0,
> >> + 0, comp_pat_index, 0),
> >> + -EINVAL);
> >> + } else {
> >> + igt_debug("Platform has no CCS, skipping compressed PAT
> >> bind check\n");
> >> + }
> > Does this test needs to be skipped here? If yes you need to use
> > igt_skip And handle the resource cleanup
> No. The test still has a valid positive path on platforms without CCS:
> it verifies that binding with the uncompressed PAT index succeeds. Only the
> compressed-path assertion is not applicable when HAS_FLATCCS(dev_id) is
> false, so I kept the test running and added a debug log to make that explicit.
> Skipping the test with igt_skip would drop that coverage.
>
Reviewed-by: Pravalika Gurram <pravalika.gurram@intel.com>
> >> + /* Uncompressed bind must always succeed */
> >> igt_assert_eq(__xe_vm_bind(fd, vm, 0, bo, 0, 0x100000,
> >> size, 0, 0, NULL, 0,
> >> 0, uncomp_pat_index, 0),
> >> --
> >> 2.52.0