Hi, Douglas: Douglas Anderson <dianders@xxxxxxxxxxxx> 於 2025年1月17日 週五 上午1:43寫道： > > The function mtk_dp_wait_hpd_asserted() may be called before the > `mtk_dp->drm_dev` pointer is assigned in mtk_dp_bridge_attach(). > Specifically it can be called via this callpath: > - mtk_edp_wait_hpd_asserted > - [panel probe] > - dp_aux_ep_probe > > Using "drm" level prints anywhere in this callpath causes a NULL > pointer dereference. Change the error message directly in > mtk_dp_wait_hpd_asserted() to dev_err() to avoid this. Also change the > error messages in mtk_dp_parse_capabilities(), which is called by > mtk_dp_wait_hpd_asserted(). > > While touching these prints, also add the error code to them to make > future debugging easier. Applied to mediatek-drm-next [1], thanks. [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/log/?h=mediatek-drm-next Regards, Chun-Kuang. > > Fixes: 7eacba9a083b ("drm/mediatek: dp: Add .wait_hpd_asserted() for AUX bus") > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > --- > Unfortunately, I have only been able to compile-time test this code. I > hit the NULL pointer dereference on a device that's nowhere near > upstream and it was running (sigh) a heavily modified copy of this > code where the eDP stuff has been forked out of DP. Specifically, you > can see <https://crrev.com/c/6073744>. It's pretty easy to understand > that the same problem affects both codebases though, so I'm posting > this "blind" in the hopes to at least fix upstream. > > I'll also note that the fact that mtk_edp_wait_hpd_asserted() calls > mtk_dp_parse_capabilities() feels weird/wrong to me based on other eDP > code I've worked on, but I've only barely looked at the Mediatek > driver and perhaps others have already debated this. In any case, > that's not directly related to this patch. > > drivers/gpu/drm/mediatek/mtk_dp.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c > index 0687672f0e52..ccd104d8851f 100644 > --- a/drivers/gpu/drm/mediatek/mtk_dp.c > +++ b/drivers/gpu/drm/mediatek/mtk_dp.c > @@ -1763,7 +1763,7 @@ static int mtk_dp_parse_capabilities(struct mtk_dp *mtk_dp) > > ret = drm_dp_dpcd_readb(&mtk_dp->aux, DP_MSTM_CAP, &val); > if (ret < 1) { > - drm_err(mtk_dp->drm_dev, "Read mstm cap failed\n"); > + dev_err(mtk_dp->dev, "Read mstm cap failed: %zd\n", ret); > return ret == 0 ? -EIO : ret; > } > > @@ -1773,7 +1773,7 @@ static int mtk_dp_parse_capabilities(struct mtk_dp *mtk_dp) > DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0, > &val); > if (ret < 1) { > - drm_err(mtk_dp->drm_dev, "Read irq vector failed\n"); > + dev_err(mtk_dp->dev, "Read irq vector failed: %zd\n", ret); > return ret == 0 ? -EIO : ret; > } > > @@ -2056,7 +2056,7 @@ static int mtk_dp_wait_hpd_asserted(struct drm_dp_aux *mtk_aux, unsigned long wa > > ret = mtk_dp_parse_capabilities(mtk_dp); > if (ret) { > - drm_err(mtk_dp->drm_dev, "Can't parse capabilities\n"); > + dev_err(mtk_dp->dev, "Can't parse capabilities: %d\n", ret); > return ret; > } > > -- > 2.48.0.rc2.279.g1de40edade-goog >
