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

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

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 john@metanate.com Reviewed-by: Chris Zhong zyw@rock-chips.com

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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;

... }

Sean

-- 2.11.0.197.gb556de5.dirty

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