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

["Yadav, Sanjay Kumar" <sanjay.kumar.yadav@intel.com>]

On 03-03-2026 16:53, Gurram, Pravalika wrote:
>
>> -----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>

Thanks for the prompt review and your time

-Sanjay

>>>> +	/* 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