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

John Keeping
2017-01-31T11:56:34Z

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:
> > 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>
> > ---
> > 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.