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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tom Rix <trix@redhat.com>,
        Patrik Jakobsson <patrik.r.jakobsson@gmail.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 031/139] drm/gma500: fix error check
Date:   Tue, 27 Oct 2020 14:48:45 +0100
Message-Id: <20201027134903.613844852@linuxfoundation.org>
In-Reply-To: <20201027134902.130312227@linuxfoundation.org>
References: <20201027134902.130312227@linuxfoundation.org>
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From: Tom Rix <trix@redhat.com>

[ Upstream commit cdd296cdae1af2d27dae3fcfbdf12c5252ab78cf ]

Reviewing this block of code in cdv_intel_dp_init()

ret = cdv_intel_dp_aux_native_read(gma_encoder, DP_DPCD_REV, ...

cdv_intel_edp_panel_vdd_off(gma_encoder);
if (ret == 0) {
	/* if this fails, presume the device is a ghost */
	DRM_INFO("failed to retrieve link info, disabling eDP\n");
	drm_encoder_cleanup(encoder);
	cdv_intel_dp_destroy(connector);
	goto err_priv;
} else {

The (ret == 0) is not strict enough.
cdv_intel_dp_aux_native_read() returns > 0 on success
otherwise it is failure.

So change to <=

Fixes: d112a8163f83 ("gma500/cdv: Add eDP support")

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200805205911.20927-1-trix@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/gma500/cdv_intel_dp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/gma500/cdv_intel_dp.c b/drivers/gpu/drm/gma500/cdv_intel_dp.c
index c52f9adf5e04c..7ec4e3fbafd8c 100644
--- a/drivers/gpu/drm/gma500/cdv_intel_dp.c
+++ b/drivers/gpu/drm/gma500/cdv_intel_dp.c
@@ -2121,7 +2121,7 @@ cdv_intel_dp_init(struct drm_device *dev, struct psb_intel_mode_device *mode_dev
 					       intel_dp->dpcd,
 					       sizeof(intel_dp->dpcd));
 		cdv_intel_edp_panel_vdd_off(gma_encoder);
-		if (ret == 0) {
+		if (ret <= 0) {
 			/* if this fails, presume the device is a ghost */
 			DRM_INFO("failed to retrieve link info, disabling eDP\n");
 			cdv_intel_dp_encoder_destroy(encoder);
-- 
2.25.1