linux-kernel - Re: [PATCH 1/1] drm/tegra: Add guard to avoid double disable/enable of RGB outputs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140211205443.GB1895@mithrandir>
Date:	Tue, 11 Feb 2014 21:54:45 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Erik Faye-Lund <kusmabite@...il.com>
Cc:	Dmitry Osipenko <digetx@...il.com>, tbergstrom@...dia.com,
	airlied@...ux.ie, swarren@...dotorg.org,
	dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] drm/tegra: Add guard to avoid double disable/enable
 of RGB outputs

On Tue, Feb 11, 2014 at 08:13:14PM +0100, Erik Faye-Lund wrote:
> On Tue, Feb 11, 2014 at 6:12 PM, Dmitry Osipenko <digetx@...il.com> wrote:
> > Add guard to check whether RGB output is already enabled in the way it's
> > done for HDMI output. Fixes possible hang on trying to disable output twice
> > (first time during driver probe and second on fb registering).
> >
> > Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> > ---
> >  drivers/gpu/drm/tegra/rgb.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/tegra/rgb.c b/drivers/gpu/drm/tegra/rgb.c
> > index 338f7f6..0266fb4 100644
> > --- a/drivers/gpu/drm/tegra/rgb.c
> > +++ b/drivers/gpu/drm/tegra/rgb.c
> > @@ -15,6 +15,7 @@
> >  struct tegra_rgb {
> >         struct tegra_output output;
> >         struct tegra_dc *dc;
> > +       bool enabled;
> >
> >         struct clk *clk_parent;
> >         struct clk *clk;
> > @@ -89,6 +90,9 @@ static int tegra_output_rgb_enable(struct tegra_output *output)
> >         struct tegra_rgb *rgb = to_rgb(output);
> >         unsigned long value;
> >
> > +       if (rgb->enabled)
> > +               return 0;
> > +
> >         tegra_dc_write_regs(rgb->dc, rgb_enable, ARRAY_SIZE(rgb_enable));
> >
> >         value = DE_SELECT_ACTIVE | DE_CONTROL_NORMAL;
> > @@ -122,6 +126,8 @@ static int tegra_output_rgb_enable(struct tegra_output *output)
> >         tegra_dc_writel(rgb->dc, GENERAL_ACT_REQ << 8, DC_CMD_STATE_CONTROL);
> >         tegra_dc_writel(rgb->dc, GENERAL_ACT_REQ, DC_CMD_STATE_CONTROL);
> >
> > +       rgb->enabled = true;
> > +
> >         return 0;
> >  }
> >
> > @@ -130,6 +136,9 @@ static int tegra_output_rgb_disable(struct tegra_output *output)
> >         struct tegra_rgb *rgb = to_rgb(output);
> >         unsigned long value;
> >
> > +       if (!rgb->enabled)
> > +               return 0;
> > +
> >         value = tegra_dc_readl(rgb->dc, DC_CMD_DISPLAY_POWER_CONTROL);
> >         value &= ~(PW0_ENABLE | PW1_ENABLE | PW2_ENABLE | PW3_ENABLE |
> >                    PW4_ENABLE | PM0_ENABLE | PM1_ENABLE);
> > @@ -144,6 +153,8 @@ static int tegra_output_rgb_disable(struct tegra_output *output)
> >
> >         tegra_dc_write_regs(rgb->dc, rgb_disable, ARRAY_SIZE(rgb_disable));
> >
> > +       rgb->enabled = false;
> > +
> >         return 0;
> >  }
> >
> 
> Wouldn't it make more sense to make "enabled" and int that counts how
> many times tegra_output_rgb_enable has been called? That way you can
> have tegra_output_rgb_disable only really disable the display once the
> same amount of disables have been performed...

I don't think that will work. Calls to tegra_output_rgb_enable/disable()
and the .enable/disable for any other outputs aren't guaranteed to be
balanced. Therefore reference counting the enables and disables will
break things.

Thinking about it, maybe the current interface to outputs isn't the best
solution. It's simple and with the guards in place it works pretty well.
Perhaps if I can find some spare time I'll investigate whether something
a little cleaner can be done.

Thierry

Content of type "application/pgp-signature" skipped