[PATCH v3 10/24] drm/rockchip: dw-mipi-dsi: don't assume buffer is aligned

On Mon, 30 Jan 2017 15:08:11 -0500, Sean Paul wrote:

On Sun, Jan 29, 2017 at 01:24:30PM +0000, John Keeping wrote:

quoted

By dereferencing the MIPI command buffer as a u32* we rely on it being
correctly aligned on ARM, but this may not be the case.  Copy it into a
stack variable that will be correctly aligned.

Signed-off-by: John Keeping <redacted>
Reviewed-by: Chris Zhong <redacted>
---
v3:
- Add Chris' Reviewed-by
Unchanged in v2

 drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
index 03fc096fe1bd..ddbc037e7ced 100644
--- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
+++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c

@@ -607,10 +607,10 @@ static int dw_mipi_dsi_dcs_short_write(struct dw_mipi_dsi *dsi,
 static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
 				      const struct mipi_dsi_msg *msg)
 {
-	const u32 *tx_buf = msg->tx_buf;
-	int len = msg->tx_len, pld_data_bytes = sizeof(*tx_buf), ret;
+	const u8 *tx_buf = msg->tx_buf;
+	int len = msg->tx_len, pld_data_bytes = sizeof(u32), ret;
 	u32 hdr_val = GEN_HDATA(msg->tx_len) | GEN_HTYPE(msg->type);
-	u32 remainder = 0;
+	u32 remainder;
 	u32 val;
 
 	if (msg->tx_len < 3) {

@@ -621,12 +621,14 @@ static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
 
 	while (DIV_ROUND_UP(len, pld_data_bytes)) {
 		if (len < pld_data_bytes) {
+			remainder = 0;
 			memcpy(&remainder, tx_buf, len);
 			dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
 			len = 0;
 		} else {
-			dsi_write(dsi, DSI_GEN_PLD_DATA, *tx_buf);
-			tx_buf++;
+			memcpy(&remainder, tx_buf, pld_data_bytes);
+			dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
+			tx_buf += pld_data_bytes;
 			len -= pld_data_bytes;
 		}  

You can clean this up further by removing a couple of the locals, the
conditional and the division:

while(len < msg->tx_len) {
        size_t to_write = MIN(msg->tx_len - len, sizeof(remainder));

        memcpy(&remainder, msg->tx_buf + len, to_write);
        dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
        len += to_write;

        ...
}

That's a nice simplification, but it's more than I was trying to do with
this patch.  I can add a cleanup patch on top to simplify the function,
but I don't have that much time to spend on this at the moment and I'd
rather not block this fix because the original code structure could be
improved.