> -----Original Message-----
> From: dri-devel <dri-devel-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of Hyun
> Kwon
> Sent: Thursday, July 30, 2020 7:33 PM
> To: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>; dri-
> devel@xxxxxxxxxxxxxxxxxxxxx; Daniel Vetter <daniel.vetter@xxxxxxxxxxx>
> Subject: Re: [PATCH v2 1/1] drm: xlnx: zynqmp: Use switch - case for link rate
> downshift
>
> Hi Laurent,
>
> Thanks for the comment.
>
> On Thu, Jul 30, 2020 at 04:12:46PM -0700, Laurent Pinchart wrote:
> > Hi Hyun,
> >
> > Thank you for the patch.
> >
> > On Wed, Jul 29, 2020 at 04:30:45PM -0700, Hyun Kwon wrote:
> > > Use switch - case to downshift from the current link rate. It's a small
> > > loop now, so fine to be replaced with switch - case. With a loop, it is
> > > confusing and hard to follow as reported below.
> > >
> > > The patch d76271d22694: "drm: xlnx: DRM/KMS driver for Xilinx ZynqMP
> > > DisplayPort Subsystem" from Jul 7, 2018, leads to the following
> > > static checker warning:
> > >
> > > drivers/gpu/drm/xlnx/zynqmp_dp.c:594 zynqmp_dp_mode_configure()
> > > error: iterator underflow 'bws' (-1)-2
> > >
> > > Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > > Signed-off-by: Hyun Kwon <hyun.kwon@xxxxxxxxxx>
> > > ---
> > > v2
> > > - Convert the for loop into switch - case
> > > ---
> > > ---
> > > drivers/gpu/drm/xlnx/zynqmp_dp.c | 29 ++++++++++++++++-------------
> > > 1 file changed, 16 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > index b735072..5d6adeaa 100644
> > > --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > > @@ -567,34 +567,37 @@ static int zynqmp_dp_mode_configure(struct
> zynqmp_dp *dp, int pclock,
> > > u8 current_bw)
> > > {
> > > int max_rate = dp->link_config.max_rate;
> > > - u8 bws[3] = { DP_LINK_BW_1_62, DP_LINK_BW_2_7,
> DP_LINK_BW_5_4 };
> > > + u8 bw_code;
> > > u8 max_lanes = dp->link_config.max_lanes;
> > > u8 max_link_rate_code = drm_dp_link_rate_to_bw_code(max_rate);
> > > u8 bpp = dp->config.bpp;
> > > u8 lane_cnt;
> > > - s8 i;
> > >
> > > - if (current_bw == DP_LINK_BW_1_62) {
> > > + /* Downshift from current one */
> >
> > Maybe "Downshift from the current bandwidth" ?
> >
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> >
>
> I agree. I'll fix and add the tag.
>
Applied to drm-misc-next-fixes.
Thanks,
-hyun
> Thanks!
>
> -hyun
>
> > > + switch (current_bw) {
> > > + case DP_LINK_BW_5_4:
> > > + bw_code = DP_LINK_BW_2_7;
> > > + break;
> > > + case DP_LINK_BW_2_7:
> > > + bw_code = DP_LINK_BW_1_62;
> > > + break;
> > > + case DP_LINK_BW_1_62:
> > > dev_err(dp->dev, "can't downshift. already lowest link rate\n");
> > > return -EINVAL;
> > > - }
> > > -
> > > - for (i = ARRAY_SIZE(bws) - 1; i >= 0; i--) {
> > > - if (current_bw && bws[i] >= current_bw)
> > > - continue;
> > > -
> > > - if (bws[i] <= max_link_rate_code)
> > > - break;
> > > + default:
> > > + /* If not given, start with max supported */
> > > + bw_code = max_link_rate_code;
> > > + break;
> > > }
> > >
> > > for (lane_cnt = 1; lane_cnt <= max_lanes; lane_cnt <<= 1) {
> > > int bw;
> > > u32 rate;
> > >
> > > - bw = drm_dp_bw_code_to_link_rate(bws[i]);
> > > + bw = drm_dp_bw_code_to_link_rate(bw_code);
> > > rate = zynqmp_dp_max_rate(bw, lane_cnt, bpp);
> > > if (pclock <= rate) {
> > > - dp->mode.bw_code = bws[i];
> > > + dp->mode.bw_code = bw_code;
> > > dp->mode.lane_cnt = lane_cnt;
> > > dp->mode.pclock = pclock;
> > > return dp->mode.bw_code;
> >
> > --
> > Regards,
> >
> > Laurent Pinchart
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