Patch "drm/radeon: drop register readback in cayman_cp_int_cntl_setup" has been added to the 4.8-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    drm/radeon: drop register readback in cayman_cp_int_cntl_setup

to the 4.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-radeon-drop-register-readback-in-cayman_cp_int_cntl_setup.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 537b4b462caa8bfb9726d9695b8e56e2d5e6b41e Mon Sep 17 00:00:00 2001
From: Lucas Stach <dev@lynxeye.de>
Date: Mon, 24 Oct 2016 23:32:04 +0200
Subject: drm/radeon: drop register readback in cayman_cp_int_cntl_setup
MIME-Version: 1.0
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From: Lucas Stach <dev@lynxeye.de>

commit 537b4b462caa8bfb9726d9695b8e56e2d5e6b41e upstream.

The read is taking a considerable amount of time (about 50us on this
machine). The register does not ever hold anything other than the ring
ID that is updated in this exact function, so there is no need for
the read modify write cycle.

This chops off a big chunk of the time spent in hardirq disabled
context, as this function is called multiple times in the interrupt
handler. With this change applied radeon won't show up in the list
of the worst IRQ latency offenders anymore, where it was a regular
before.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/radeon/ni.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/gpu/drm/radeon/ni.c
+++ b/drivers/gpu/drm/radeon/ni.c
@@ -1396,9 +1396,7 @@ static void cayman_pcie_gart_fini(struct
 void cayman_cp_int_cntl_setup(struct radeon_device *rdev,
 			      int ring, u32 cp_int_cntl)
 {
-	u32 srbm_gfx_cntl = RREG32(SRBM_GFX_CNTL) & ~3;
-
-	WREG32(SRBM_GFX_CNTL, srbm_gfx_cntl | (ring & 3));
+	WREG32(SRBM_GFX_CNTL, RINGID(ring));
 	WREG32(CP_INT_CNTL, cp_int_cntl);
 }
 


Patches currently in stable-queue which might be from dev@lynxeye.de are

queue-4.8/drm-radeon-drop-register-readback-in-cayman_cp_int_cntl_setup.patch