On Wed, Jul 17, 2019 at 07:20:29PM +0300, Ville Syrjälä wrote: > On Wed, Jul 17, 2019 at 12:01:48PM -0400, Sean Paul wrote: > > From: Sean Paul <seanpaul@xxxxxxxxxxxx> > > > > Although the DisplayPort spec explicitly calls out the 1.62/2.7/5.4/8.1 > > link rates, the value of LINK_BW_SET is calculated. The DisplayPort > > spec says "Main-Link Bandwidth Setting = Value x 0.27Gbps/lane". > > > > A bridge that we're looking to upstream uses 6.75Gbps rate (value 0x19) > > [1], and that precludes it from using these functions. > > The DP spec has this note: > "A MyDP Source device, upon reading the MAX_LINK_RATE register of the > downstream DPRX programmed to 19h (which can be the case only for a > MyDP-to-Legacy or MyDP-to-DP lane count converter) can program the > LINK_BW_SET register (DPCD Address 00100h) to 19h to enable 6.75Gbps/lane." > > Which I guess is the thing you're seeing. Thanks for digging this up. The spec I reviewed didn't have this, but it did mention some more esoteric exceptions to the Big 4 (it might not even have HBR3 either, I'm not sure. /me really needs to get up-to-date specs) defined rates. I'll add this to my commit message when I apply it. > > But I think the patch makes sense in any case. Otherwise anyone who > plugs in some new display to a machine with an old kernel will likely > get that WARN. Assuming the driver correctly limits the max link rate > based on the source device capabilities there's no harm in letting > the sink declare higher limits. Yep, and not only the WARN, but they'll also get 1.62Gbps rate/code. So calculating the value seems like the safer route to take. > > Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> Thanks! I'll apply it to drm-misc-next. Sean > > > > > This patch calculates the values according to spec instead of > > restricting these values to one of the DP_LINK_BW_* #defines. > > > > No functional change for the well-defined values, but we lose the > > warning for ill-defined bw values. > > > > Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx> > > > > [1] https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1689251/2/drivers/gpu/drm/bridge/analogix/anx7625.c#636 > > --- > > drivers/gpu/drm/drm_dp_helper.c | 31 ++++--------------------------- > > 1 file changed, 4 insertions(+), 27 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c > > index 0b994d083a89..ffc68d305afe 100644 > > --- a/drivers/gpu/drm/drm_dp_helper.c > > +++ b/drivers/gpu/drm/drm_dp_helper.c > > @@ -152,38 +152,15 @@ EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay); > > > > u8 drm_dp_link_rate_to_bw_code(int link_rate) > > { > > - switch (link_rate) { > > - default: > > - WARN(1, "unknown DP link rate %d, using %x\n", link_rate, > > - DP_LINK_BW_1_62); > > - /* fall through */ > > - case 162000: > > - return DP_LINK_BW_1_62; > > - case 270000: > > - return DP_LINK_BW_2_7; > > - case 540000: > > - return DP_LINK_BW_5_4; > > - case 810000: > > - return DP_LINK_BW_8_1; > > - } > > + /* Spec says link_bw = link_rate / 0.27Gbps */ > > + return link_rate / 27000; > > } > > EXPORT_SYMBOL(drm_dp_link_rate_to_bw_code); > > > > int drm_dp_bw_code_to_link_rate(u8 link_bw) > > { > > - switch (link_bw) { > > - default: > > - WARN(1, "unknown DP link BW code %x, using 162000\n", link_bw); > > - /* fall through */ > > - case DP_LINK_BW_1_62: > > - return 162000; > > - case DP_LINK_BW_2_7: > > - return 270000; > > - case DP_LINK_BW_5_4: > > - return 540000; > > - case DP_LINK_BW_8_1: > > - return 810000; > > - } > > + /* Spec says link_rate = link_bw * 0.27Gbps */ > > + return link_bw * 27000; > > } > > EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate); > > > > -- > > Sean Paul, Software Engineer, Google / Chromium OS > > > > _______________________________________________ > > dri-devel mailing list > > dri-devel@xxxxxxxxxxxxxxxxxxxxx > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > -- > Ville Syrjälä > Intel -- Sean Paul, Software Engineer, Google / Chromium OS _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
