linux-kernel - Re: [PATCH v3 01/12] drm/bridge: Fix the stop condition of drm_bridge_chain_pre

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Message-ID: <CAD=FV=UN38EiYMiwNjysBS6dReKDaf+g2GcgaVt9iF1mTRKg7A@mail.gmail.com>
Date:   Wed, 14 Apr 2021 18:19:13 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sam Ravnborg <sam@...nborg.org>,
        Linus W <linus.walleij@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Clark <robdclark@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Steev Klimaszewski <steev@...i.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 01/12] drm/bridge: Fix the stop condition of drm_bridge_chain_pre_enable()

Hi,

On Sun, Apr 4, 2021 at 5:50 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Doug,
>
> Thank you for the patch.
>
> On Fri, Apr 02, 2021 at 03:28:35PM -0700, Douglas Anderson wrote:
> > The drm_bridge_chain_pre_enable() is not the proper opposite of
> > drm_bridge_chain_post_disable(). It continues along the chain to
> > _before_ the starting bridge. Let's fix that.
> >
> > Fixes: 05193dc38197 ("drm/bridge: Make the bridge chain a double-linked list")
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>
> > ---
> >
> > (no changes since v1)
> >
> >  drivers/gpu/drm/drm_bridge.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > index 64f0effb52ac..044acd07c153 100644
> > --- a/drivers/gpu/drm/drm_bridge.c
> > +++ b/drivers/gpu/drm/drm_bridge.c
> > @@ -522,6 +522,9 @@ void drm_bridge_chain_pre_enable(struct drm_bridge *bridge)
> >       list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
> >               if (iter->funcs->pre_enable)
> >                       iter->funcs->pre_enable(iter);
> > +
> > +             if (iter == bridge)
> > +                     break;
>
> This looks good as it matches drm_atomic_bridge_chain_disable().
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

Thanks for your review here and several of the other patches. Can you
suggest any plan for getting them landed? It would at least be nice to
get the non-controversial ones landed.


> I'm curious though, given that the bridge passed to the function should
> be the one closest to the encoder, does this make a difference ?

Yes, that's how I discovered it originally. Let's see. So if I don't
have this patch but have the rest of the series then I get a splat at
bootup. This shows that dsi_mgr_bridge_pre_enable() must be "earlier"
in the chain than my bridge chip. Here's the splat:

 msm_dsi_host_get_phy_clk_req: unable to calc clk rate, -22
 ------------[ cut here ]------------
 disp_cc_mdss_ahb_clk status stuck at 'off'
 WARNING: CPU: 7 PID: 404 at drivers/clk/qcom/clk-branch.c:92
clk_branch_toggle+0x194/0x280
 Modules linked in: joydev
 CPU: 7 PID: 404 Comm: frecon Tainted: G    B             5.12.0-rc3-lockdep+ #2
 Hardware name: Google Lazor (rev1 - 2) with LTE (DT)
 pstate: 60400089 (nZCv daIf +PAN -UAO -TCO BTYPE=--)
 pc : clk_branch_toggle+0x194/0x280
 lr : clk_branch_toggle+0x190/0x280
 ...
 Call trace:
  clk_branch_toggle+0x194/0x280
  clk_branch2_enable+0x28/0x34
  clk_core_enable+0x2f4/0x6b4
  clk_enable+0x54/0x74
  dsi_phy_enable_resource+0x80/0xd8
  msm_dsi_phy_enable+0xa8/0x4a8
  enable_phy+0x9c/0xf4
  dsi_mgr_bridge_pre_enable+0x23c/0x4b0
  drm_bridge_chain_pre_enable+0xac/0xe4
  ti_sn_bridge_connector_get_modes+0x134/0x1b8
  drm_helper_probe_single_connector_modes+0x49c/0x1358
  drm_mode_getconnector+0x460/0xe98
  drm_ioctl_kernel+0x144/0x228
  drm_ioctl+0x418/0x7cc
  drm_compat_ioctl+0x1bc/0x230
  __arm64_compat_sys_ioctl+0x14c/0x188
  el0_svc_common+0x128/0x23c
  do_el0_svc_compat+0x50/0x60
  el0_svc_compat+0x24/0x34
  el0_sync_compat_handler+0xc0/0xf0
  el0_sync_compat+0x174/0x180