lkml.org 
[lkml]   [2021]   [Dec]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH] drm/dp: Actually read Adjust Request Post Cursor2 register
    From


    On 2021-12-09 01:23, Kees Cook wrote:
    > On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote:
    >> On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote:
    >>> The link_status array was not large enough to read the Adjust Request
    >>> Post Cursor2 register. Adjust the size to include it. Found with a
    >>> -Warray-bounds build:
    >>>
    >>> drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor':
    >>> drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds]
    >>> 59 | return link_status[r - DP_LANE0_1_STATUS];
    >>> | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
    >>> drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status'
    >>> 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
    >>> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    >>>
    >>> Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments")
    >>> Signed-off-by: Kees Cook <keescook@chromium.org>
    >>
    >> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3
    >> published in 2014, and Tegra is the only user of
    >> drm_dp_get_adjust_request_post_cursor().
    >
    > I see POST_CURSOR2 is used here too:
    >
    > drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
    >

    Looks like we read and parse that in the admgpu driver without
    using drm_dp_get_adjust_request_post_cursor.

    I don't have a strong feeling but I liked your original
    patch a bit better. I'm not sure what it means when part
    of a spec is deprecated. Once a spec is written display
    vendors might implement it. We should make sure that
    displays like that are always handled in a sane manner.

    Harry

    > Here's a version of that for tegra (untested):
    >
    >
    > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
    > index 23f9073bc473..c9528aa62c9c 100644
    > --- a/drivers/gpu/drm/drm_dp_helper.c
    > +++ b/drivers/gpu/drm/drm_dp_helper.c
    > @@ -144,16 +144,6 @@ u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE],
    > }
    > EXPORT_SYMBOL(drm_dp_get_adjust_tx_ffe_preset);
    >
    > -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
    > - unsigned int lane)
    > -{
    > - unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2;
    > - u8 value = dp_link_status(link_status, offset);
    > -
    > - return (value >> (lane << 1)) & 0x3;
    > -}
    > -EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor);
    > -
    > static int __8b10b_clock_recovery_delay_us(const struct drm_dp_aux *aux, u8 rd_interval)
    > {
    > if (rd_interval > 4)
    > diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c
    > index 70dfb7d1dec5..f5535eb04c6b 100644
    > --- a/drivers/gpu/drm/tegra/dp.c
    > +++ b/drivers/gpu/drm/tegra/dp.c
    > @@ -549,6 +549,15 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link,
    > {
    > struct drm_dp_link_train_set *adjust = &link->train.adjust;
    > unsigned int i;
    > + u8 post_cursor;
    > + int err;
    > +
    > + err = drm_dp_dpcd_read(link->aux, DP_ADJUST_REQUEST_POST_CURSOR2,
    > + &post_cursor, sizeof(post_cursor));
    > + if (err < 0) {
    > + DRM_ERROR("failed to read post_cursor2: %d\n", err);
    > + post_cursor = 0;
    > + }
    >
    > for (i = 0; i < link->lanes; i++) {
    > adjust->voltage_swing[i] =
    > @@ -560,7 +569,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link,
    > DP_TRAIN_PRE_EMPHASIS_SHIFT;
    >
    > adjust->post_cursor[i] =
    > - drm_dp_get_adjust_request_post_cursor(status, i);
    > + (post_cursor >> (i << 1)) & 0x3;
    > }
    > }
    >
    > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
    > index 30359e434c3f..28378db676c8 100644
    > --- a/include/drm/drm_dp_helper.h
    > +++ b/include/drm/drm_dp_helper.h
    > @@ -1528,8 +1528,6 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI
    > int lane);
    > u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE],
    > int lane);
    > -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],
    > - unsigned int lane);
    >
    > #define DP_BRANCH_OUI_HEADER_SIZE 0xc
    > #define DP_RECEIVER_CAP_SIZE 0xf
    >
    >
    > Is that the right way to go?
    >

    \
     
     \ /
      Last update: 2021-12-09 23:21    [W:4.000 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site