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    SubjectRe: [PATCH v3 10/24] drm/rockchip: dw-mipi-dsi: don't assume buffer is aligned
    On Tue, Jan 31, 2017 at 11:56:18AM +0000, John Keeping wrote:
    > 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.

    Ok. I'm inclined to argue that writing your response probably took more time
    than the copy/paste to fix it, but *shrug*.

    Sean

    > _______________________________________________
    > dri-devel mailing list
    > dri-devel@lists.freedesktop.org
    > https://lists.freedesktop.org/mailman/listinfo/dri-devel

    --
    Sean Paul, Software Engineer, Google / Chromium OS

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