linux-kernel - Re: [PATCH 1/2] drm/rockchip: dw_hdmi: Call drm_encoder

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Date:	Mon, 07 Mar 2016 19:56:18 +0100
From:	Heiko Stübner <heiko@...ech.de>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Mark yao <mark.yao@...k-chips.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	John Keeping <john@...ping.me.uk>,
	David Airlie <airlied@...ux.ie>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Daniel Kurtz <djkurtz@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] drm/rockchip: dw_hdmi: Call drm_encoder_cleanup() in error path

Hi Doug,

Am Montag, 7. März 2016, 10:49:53 schrieb Doug Anderson:
> On Mon, Mar 7, 2016 at 9:57 AM, Heiko Stübner <heiko@...ech.de> wrote:
> > Am Montag, 7. März 2016, 09:36:07 schrieb Doug Anderson:
> >> Hi,
> >> 
> >> On Mon, Mar 7, 2016 at 12:37 AM, Mark yao <mark.yao@...k-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@...omium.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.
> > 
> > I don't think handing off the cleanup responsibility is really in question
> > here. I.e. I do believe it should also be fine to expect (as definition)
> > the core driver to cleanup the encoder _after_ it sucessfully claimed it
> > in dw_hdmi_bind().
> > 
> > We do the same in the rockchip power-domains, handing off the struct clk-
> > pointer to the pm_clk stuff (due to the clk-pointer being unique
> > per-device
> > nowadays).
> > 
> > So just making sure it is sucessfully handed off should also be ok.
> 
> If I understand correctly, that means you'd be OK with the original
> patch I posted?  In that case cleanup continues to happen in the main
> dw-hdmi.c if dw_hdmi_bind() succeeds and my patch fixes the cleanup
> when dw_hdmi_bind() fails (and thus cleanup responsibility was not
> handed off).

correct. I don't see the need to duplicate the cleanup (+added infrastructure 
to actually get the encoder in unbind) in all instances, if we just define that 
the dw_hdmi core takes control of the encoder _after_ it sucessfully bound.

So only if dw_hdmi_bind() fails does the hw-specific instance need to clean up 
the encoder it created.


> Also: I noticed that Russell also didn't seem to say that my original
> patch was bad.  I think he just said that he didn't like John
> Keeping's suggestion.

that was my reading as well.


Heiko