Re: [PATCH 1/2] drm/rockchip: dw_hdmi: Call drm_encoder_cleanup() in error path

Doug Anderson
2016-03-07T17:36:07Z

Hi,

On Mon, Mar 7, 2016 at 12:37 AM, Mark yao <mark.yao@rock-chips.com> wrote:
> On 2016年03月05日 20:39, Russell King - ARM Linux wrote:
>>
>> On Sat, Mar 05, 2016 at 12:11:16PM +0000, John Keeping wrote:
>>>
>>> On Fri, Mar 04, 2016 at 03:22:01PM -0800, Douglas Anderson wrote:
>>>>
>>>> The drm_encoder_cleanup() was missing both from the error path of
>>>> dw_hdmi_rockchip_bind(). This caused a crash when slub_debug was
>>>> enabled and we ended up deferring probe of HDMI at boot.
>>>>
>>>> This call isn't needed from unbind() because if dw_hdmi_bind() returns
>>>> no error then it takes over the job of freeing the encoder (in
>>>> dw_hdmi_unbind).
>>>>
>>>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
>>>> ---
>>>
>>> Does dw_hdmi-imx need a similar change? I wonder if it would be cleaner
>>> to push this into dw_hdmi_bind() if it affects all of the platforms..
>>
>> I don't think moving it there would make sense - keep the initialisation
>> and cleanup together in the same file so that it's contained together.
>>
>
> I don't like this patch too, initialisation and cleanup not in the same file
> looks bad,
>
> How about:
>
> drivers/gpu/drm/bridge/dw-hdmi.c
> void dw_hdmi_unbind(struct device *dev, struct device *master, void *data)
> hdmi_writeb(hdmi, ~0, HDMI_IH_MUTE_PHY_STAT0);
>
> hdmi->connector.funcs->destroy(&hdmi->connector);
> - hdmi->encoder->funcs->destroy(hdmi->encoder);
>
> drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
> static int dw_hdmi_rockchip_bind(struct device *dev, struct device *master,
>
> - return dw_hdmi_bind(dev, master, data, encoder, iores, irq,
> plat_data);
> + ret = dw_hdmi_bind(dev, master, data, encoder, iores, irq,
> plat_data);
> + if (ret)
> + drm_encoder_cleanup(encoder);
> +
> + return ret;
> }
>
> static void dw_hdmi_rockchip_unbind(struct device *dev, struct device
> *master,
> void *data)
> {
> + drm_encoder_cleanup(...);
> return dw_hdmi_unbind(dev, master, data);
> }

That'a a reasonable suggestion in theory. ...but we run into the same
problem I've run into before with the strange relationship between
dw_hdmi and its descendants.

Specifically:

* "struct dw_hdmi", which has a pointer to encoder, is private to dw-hdmi.c

* We could get the encoder if we had a pointer to the "struct
rockchip_hdmi", but there's no way to get that. You would _think_ you
could get it back using platform_get_drvdata() because it was stashed
with platform_set_drvdata(). ...but you'd be wrong. The
platform_set_drvdata() is just there to fool you. I believe when you
call dw_hdmi_bind() it clobbers your drvdata when it calls
dev_set_drvdata(dev, hdmi);

Said another way: taking your suggestion means we need to add some way
for dw_hdmi-rockchip.c to get a pointer to the encoder from a "struct
device". We could (A) move the "struct dw_hdmi" definition to a
private header and allow dw_hdmi-rockchip.c to include it or we could
(B) add a dw_hdmi_get_encoder() API call that dw_hdmi-rockchip.c could
call.

If someone would let me know whether (A) or (B) is OK I'm happy to post a patch.

...or, of course, if I've made a mistake in all the above, feel free
to point it out.

-Doug