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From:   Doug Anderson <dianders@chromium.org>
Date:   Tue, 3 May 2022 15:45:03 -0700
Message-ID: <CAD=FV=XEgcrLYzLcPkf+n20VcMBD2BVFo++0BSaDWniDPzM2Hw@mail.gmail.com>
Subject: Re: [RFC PATCH 1/6] drm/dp: Helpers to make it easier for drivers to
 use DP AUX bus properly
To:     Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>,
        Robert Foss <robert.foss@linaro.org>,
        Hsin-Yi Wang <hsinyi@chromium.org>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Sankeerth Billakanti <quic_sbillaka@quicinc.com>,
        Philip Chen <philipchen@chromium.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>,
        Linus Walleij <linus.walleij@linaro.org>,
        Lyude Paul <lyude@redhat.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        LKML <linux-kernel@vger.kernel.org>
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Hi,

On Mon, Apr 18, 2022 at 4:10 PM Doug Anderson <dianders@chromium.org> wrote:
>
> So I guess where does that leave us? Maybe:
>
> 1. I'll add a WARN_ON() in of_dp_aux_populate_ep_devices() if there is
> more than one DP AUX endpoint with a comment explaining why we assume
> one DP AUX endpoint.
>
> 2. I'll create this new structure in drm_dp_aux_bus.h:
>
> struct dp_aux_populate_callbacks {
>   int (*done_probing)(struct drm_dp_aux *aux);
>   void (*pre_remove)(struct drm_dp_aux *aux);
> };
>
> 3. I'll add a second version of the populate functions that AUX bus
> providers can use if they want callbacks:
>
> int of_dp_aux_populate_ep_devices_cb(struct drm_dp_aux *aux,
>                                      struct dp_aux_populate_callbacks *cb);
> int devm_of_dp_aux_populate_ep_devices_cb(struct drm_dp_aux *aux,
>                                           struct dp_aux_populate_callbacks *cb);
>
> The old functions will just be changed to wrap the above and pass NULL
> for the callbacks. To me, this seems better/simpler than notifiers or
> any other scheme, but yell if you disagree.
>
> 4. I'll call the callsbacks in dp_aux_ep_probe() after a successful
> probe. I'll add a second callback and will call it in
> dp_aux_ep_remove() before passing the remove through to the panel.
>
>
> If that sounds peachy then I think it should be pretty doable.

I never heard any response about whether people liked the above, but I
went ahead and did something similar to it. It can be found at:

https://lore.kernel.org/r/20220503224029.3195306-1-dianders@chromium.org