linux-kernel - [PATCH AUTOSEL 5.19 007/105] drm/panfrost: Don't set L2_MMU

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20220811152851.1520029-7-sashal@kernel.org>
Date:   Thu, 11 Aug 2022 11:26:51 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Steven Price <steven.price@....com>,
        Sasha Levin <sashal@...nel.org>, robh@...nel.org,
        tomeu.vizoso@...labora.com, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 5.19 007/105] drm/panfrost: Don't set L2_MMU_CONFIG quirks

From: Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>

[ Upstream commit d8e53d8a4e0ae842ef5e83e0dfb0796980f710cf ]

L2_MMU_CONFIG is an implementation-defined register. Different Mali GPUs
define slightly different MAX_READS and MAX_WRITES fields, which
throttle outstanding reads and writes when set to non-zero values. When
left as zero, reads and writes are not throttled.

Both kbase and panfrost always zero these registers. Per discussion with
Steven Price, there are two reasons these quirks may be used:

1. Simulating slower memory subsystems. This use case is only of
   interest to system-on-chip designers; it is not relevant to mainline.

2. Working around broken memory subsystems. Hopefully we never see this
   case in mainline. If we do, we'll need to set this register based on
   an SoC-compatible, rather than generally matching on the GPU model.

To the best of our knowledge, these fields are zero at reset, so the
write is not necessary. Let's remove the write to aid porting to new
Mali GPUs, which have different layouts for the L2_MMU_CONFIG register.

Suggested-by: Steven Price <steven.price@....com>
Reviewed-by: Steven Price <steven.price@....com>
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220525145754.25866-8-alyssa.rosenzweig@collabora.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/panfrost/panfrost_gpu.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
index 295bef27fb55..e1a6e763d0dc 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
@@ -127,18 +127,6 @@ static void panfrost_gpu_init_quirks(struct panfrost_device *pfdev)
 	gpu_write(pfdev, GPU_TILER_CONFIG, quirks);

-	quirks = gpu_read(pfdev, GPU_L2_MMU_CONFIG);
-
-	/* Limit read & write ID width for AXI */
-	if (panfrost_has_hw_feature(pfdev, HW_FEATURE_3BIT_EXT_RW_L2_MMU_CONFIG))
-		quirks &= ~(L2_MMU_CONFIG_3BIT_LIMIT_EXTERNAL_READS |
-			    L2_MMU_CONFIG_3BIT_LIMIT_EXTERNAL_WRITES);
-	else
-		quirks &= ~(L2_MMU_CONFIG_LIMIT_EXTERNAL_READS |
-			    L2_MMU_CONFIG_LIMIT_EXTERNAL_WRITES);
-
-	gpu_write(pfdev, GPU_L2_MMU_CONFIG, quirks);
-
 	quirks = 0;
 	if ((panfrost_model_eq(pfdev, 0x860) || panfrost_model_eq(pfdev, 0x880)) &&
 	    pfdev->features.revision >= 0x2000)
-- 
2.35.1