Re: [PATCH] drm/i915/guc/slpc: Apply min softlimit correctly

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On 6/13/2023 7:25 PM, Dixit, Ashutosh wrote:
On Fri, 09 Jun 2023 15:02:52 -0700, Vinay Belgaumkar wrote:
Hi Vinay,

We were skipping when min_softlimit was equal to RPn. We need to apply
it rergardless as efficient frequency will push the SLPC min to RPe.
regardless

This will break scenarios where user sets a min softlimit < RPe before
reset and then performs a GT reset.
Can you explain the reason for the patch clearly in terms of variables in
the code, what variable has what value and what is the bug. I am not
following from the above description.

Hi Ashutosh,

Scenario being fixed here is exactly the one in i915_pm_freq_api reset/suspend subtests (currently in review). Test sets min freq to RPn and then performs a reset. It then checks if cur_freq is RPn.

Here's the sequence that shows the problem-

RPLS:/home/gta# modprobe i915
RPLS:/home/gta# echo 1 > /sys/class/drm/card0/gt/gt0/slpc_ignore_eff_freq
RPLS:/home/gta# echo 300 > /sys/class/drm/card0/gt_min_freq_mhz (RPn)
RPLS:/home/gta# cat /sys/class/drm/card0/gt_cur_freq_mhz --> cur == RPn as expected
300
RPLS:/home/gta# echo 1 > /sys/kernel/debug/dri/0/gt0/reset --> reset
RPLS:/home/gta# cat /sys/class/drm/card0/gt_min_freq_mhz --> shows the internal cached variable correctly
300
RPLS:/home/gta# cat /sys/class/drm/card0/gt_cur_freq_mhz --> actual freq being requested by SLPC (it's not RPn!!)
700

We need to sync up driver min freq value and SLPC min after a reset/suspend. Currently, we skip if the user had manually set min to RPn (this was an optimization we had before we enabled efficient freq usage).

Thanks,

Vinay.


Thanks.
--
Ashutosh


Fixes: 95ccf312a1e4 ("drm/i915/guc/slpc: Allow SLPC to use efficient frequency")

Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@xxxxxxxxx>
---
  drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
index 01b75529311c..ee9f83af7cf6 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
@@ -606,7 +606,7 @@ static int slpc_set_softlimits(struct intel_guc_slpc *slpc)
		if (unlikely(ret))
			return ret;
		slpc_to_gt(slpc)->defaults.min_freq = slpc->min_freq_softlimit;
-	} else if (slpc->min_freq_softlimit != slpc->min_freq) {
+	} else {
		return intel_guc_slpc_set_min_freq(slpc,
						   slpc->min_freq_softlimit);
	}
--
2.38.1




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