linux-kernel - [PATCH 3.19.y-ckt 219/251] drm/tegra: dpaux: Fix transfers larger than 4 bytes

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Message-Id: <1437008972-9140-220-git-send-email-kamal@canonical.com>
Date:	Wed, 15 Jul 2015 18:09:00 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Thierry Reding <treding@...dia.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 219/251] drm/tegra: dpaux: Fix transfers larger than 4 bytes

3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thierry Reding <treding@...dia.com>

commit 3c1dae0a07c651526f8e878d223a88f82caa5a50 upstream.

The DPAUX read/write FIFO registers aren't sequential in the register
space, causing transfers larger than 4 bytes to cause accesses to non-
existing FIFO registers.

Fixes: 6b6b604215c6 ("drm/tegra: Add eDP support")
Signed-off-by: Thierry Reding <treding@...dia.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/gpu/drm/tegra/dpaux.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c
index d6b55e3..a43a836 100644
--- a/drivers/gpu/drm/tegra/dpaux.c
+++ b/drivers/gpu/drm/tegra/dpaux.c
@@ -72,34 +72,32 @@ static inline void tegra_dpaux_writel(struct tegra_dpaux *dpaux,
 static void tegra_dpaux_write_fifo(struct tegra_dpaux *dpaux, const u8 *buffer,
 				   size_t size)
 {
-	unsigned long offset = DPAUX_DP_AUXDATA_WRITE(0);
 	size_t i, j;
 
-	for (i = 0; i < size; i += 4) {
-		size_t num = min_t(size_t, size - i, 4);
+	for (i = 0; i < DIV_ROUND_UP(size, 4); i++) {
+		size_t num = min_t(size_t, size - i * 4, 4);
 		unsigned long value = 0;
 
 		for (j = 0; j < num; j++)
-			value |= buffer[i + j] << (j * 8);
+			value |= buffer[i * 4 + j] << (j * 8);
 
-		tegra_dpaux_writel(dpaux, value, offset++);
+		tegra_dpaux_writel(dpaux, value, DPAUX_DP_AUXDATA_WRITE(i));
 	}
 }
 
 static void tegra_dpaux_read_fifo(struct tegra_dpaux *dpaux, u8 *buffer,
 				  size_t size)
 {
-	unsigned long offset = DPAUX_DP_AUXDATA_READ(0);
 	size_t i, j;
 
-	for (i = 0; i < size; i += 4) {
-		size_t num = min_t(size_t, size - i, 4);
+	for (i = 0; i < DIV_ROUND_UP(size, 4); i++) {
+		size_t num = min_t(size_t, size - i * 4, 4);
 		unsigned long value;
 
-		value = tegra_dpaux_readl(dpaux, offset++);
+		value = tegra_dpaux_readl(dpaux, DPAUX_DP_AUXDATA_READ(i));
 
 		for (j = 0; j < num; j++)
-			buffer[i + j] = value >> (j * 8);
+			buffer[i * 4 + j] = value >> (j * 8);
 	}
 }
 
-- 
1.9.1

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