linux-kernel - [PATCH 5.11 099/306] drm/amd/display: Fix nested FPU context in dcn21_validate

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Message-Id: <20210315135510.998406518@linuxfoundation.org>
Date:   Mon, 15 Mar 2021 14:52:42 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Holger Hoffstätte 
        <holger@...lied-asynchrony.com>,
        Alex Deucher <alexander.deucher@....com>
Subject: [PATCH 5.11 099/306] drm/amd/display: Fix nested FPU context in dcn21_validate_bandwidth()

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Holger Hoffstätte <holger@...lied-asynchrony.com>

commit 15e8b95d5f7509e0b09289be8c422c459c9f0412 upstream.

Commit 41401ac67791 added FPU wrappers to dcn21_validate_bandwidth(),
which was correct. Unfortunately a nested function alredy contained
DC_FP_START()/DC_FP_END() calls, which results in nested FPU context
enter/exit and complaints by kernel_fpu_begin_mask().
This can be observed e.g. with 5.10.20, which backported 41401ac67791
and now emits the following warning on boot:

WARNING: CPU: 6 PID: 858 at arch/x86/kernel/fpu/core.c:129 kernel_fpu_begin_mask+0xa5/0xc0
Call Trace:
 dcn21_calculate_wm+0x47/0xa90 [amdgpu]
 dcn21_validate_bandwidth_fp+0x15d/0x2b0 [amdgpu]
 dcn21_validate_bandwidth+0x29/0x40 [amdgpu]
 dc_validate_global_state+0x3c7/0x4c0 [amdgpu]

The warning is emitted due to the additional DC_FP_START/END calls in
patch_bounding_box(), which is inlined into dcn21_calculate_wm(),
its only caller. Removing the calls brings the code in line with
dcn20 and makes the warning disappear.

Fixes: 41401ac67791 ("drm/amd/display: Add FPU wrappers to dcn21_validate_bandwidth()")
Signed-off-by: Holger Hoffstätte <holger@...lied-asynchrony.com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Cc: stable@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c |    4 ----
 1 file changed, 4 deletions(-)

--- a/drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c
@@ -1062,8 +1062,6 @@ static void patch_bounding_box(struct dc
 {
 	int i;
 
-	DC_FP_START();
-
 	if (dc->bb_overrides.sr_exit_time_ns) {
 		for (i = 0; i < WM_SET_COUNT; i++) {
 			  dc->clk_mgr->bw_params->wm_table.entries[i].sr_exit_time_us =
@@ -1088,8 +1086,6 @@ static void patch_bounding_box(struct dc
 				dc->bb_overrides.dram_clock_change_latency_ns / 1000.0;
 		}
 	}
-
-	DC_FP_END();
 }
 
 void dcn21_calculate_wm(