[Intel-gfx] [PATCH] drm/i915: Fix skl_pcode_try_request function

[Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>]

Currently skl_pcode_try_request function doesn't
properly handle return value it gets from
snb_pcode_rw, but treats status != 0 as success,
returning true, which basically doesn't allow
to use retry/timeout mechanisms if PCode happens
to be busy and returns EGAIN or some other status
code not equal to 0.

We saw this on real hw and also tried simulating this
by always returning -EAGAIN from snb_pcode_rw for 6 times, which
currently will just result in false success, while it should
have tried until timeout is reached:

[   22.357729] i915 0000:00:02.0: [drm:intel_cdclk_dump_config [i915]] Changing CDCLK to
307200 kHz, VCO 614400 kHz, ref 38400 kHz, bypass 19200 kHz, voltage level 0
[   22.357831] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 1
[   22.357892] i915 0000:00:02.0: [drm:skl_pcode_request [i915]] Success, exiting
[   22.357936] i915 0000:00:02.0: [drm] ERROR Failed to inform PCU about cdclk change (err -11, freq 307200)

We see en error because higher level api, still notices that status was wrong,
however we still did try only once.

We fix it by requiring _both_ the status to be 0 and
request/reply match for success(true) and function
should return failure(false) if either status turns
out to be EAGAIN, EBUSY or whatever or reply/request
masks do not match.

So now we see this in the logs:

[   22.318667] i915 0000:00:02.0: [drm:intel_cdclk_dump_config [i915]] Changing CDCLK to
307200 kHz, VCO 614400 kHz, ref 38400 kHz, bypass 19200 kHz, voltage level 0
[   22.318782] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 1
[   22.318849] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 2
[   22.319006] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 3
[   22.319091] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 4
[   22.319158] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 5
[   22.319224] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 6

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
---
 drivers/gpu/drm/i915/intel_pcode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_pcode.c b/drivers/gpu/drm/i915/intel_pcode.c
index 391a37492ce5..fb6c43e8a02f 100644
--- a/drivers/gpu/drm/i915/intel_pcode.c
+++ b/drivers/gpu/drm/i915/intel_pcode.c
@@ -136,7 +136,7 @@ static bool skl_pcode_try_request(struct drm_i915_private *i915, u32 mbox,
 {
 	*status = __snb_pcode_rw(i915, mbox, &request, NULL, 500, 0, true);
 
-	return *status || ((request & reply_mask) == reply);
+	return (*status == 0) && ((request & reply_mask) == reply);
 }
 
 /**
-- 
2.24.1.485.gad05a3d8e5