Re: [PATCH] drm/bridge: ti-sn65dsi86: fix a ternary type promotion bug

Robert Foss
2021-05-18T13:21:11Z

Hey Dan,

Thanks for submitting this.

On Tue, 18 May 2021 at 11:20, Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> The ti_sn_aux_transfer() function returns ssize_t (signed long). It's
> supposed to return negative error codes or the number of bytes
> transferred. The "ret" variable is int and the "len" variable is
> unsigned int.
>
> The problem is that with a ternary like this, the negative int is first
> type promoted to unsigned int to match "len" at this point it is a high
> positive value. Then when it is type promoted to ssize_t (s64) it
> remains a high positive value instead of sign extending and becoming a
> negative again.
>
> Fix this by removing the ternary.
>
> Fixes: b137406d9679 ("drm/bridge: ti-sn65dsi86: If refclk, DP AUX can happen w/out pre-enable")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> drivers/gpu/drm/bridge/ti-sn65dsi86.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index bb0a0e1c6341..45a2969afb2b 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -1042,7 +1042,9 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
> pm_runtime_mark_last_busy(pdata->dev);
> pm_runtime_put_autosuspend(pdata->dev);
>
> - return ret ? ret : len;
> + if (ret)
> + return ret;
> + return len;
> }
>

Reviewed-by: Robert Foss <robert.foss@linaro.org>

Applying to drm-misc-fixes.