linux-kernel - Re: [PATCH] drm/arcpgu: use .mode_fixup instead of .atomic

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Date:   Fri, 3 Mar 2017 13:27:30 +0000
From:   Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:     "daniel@...ll.ch" <daniel@...ll.ch>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "airlied@...ux.ie" <airlied@...ux.ie>
Subject: Re: [PATCH] drm/arcpgu: use .mode_fixup instead of .atomic_check

Hi Daniel,

On Thu, 2017-03-02 at 20:54 +0100, Daniel Vetter wrote:
> On Thu, Mar 02, 2017 at 08:27:54PM +0300, Alexey Brodkin wrote:
> > 
> > Since we cannot always generate exactly requested pixel clock
> > there's not much sense in checking requested_clock == clk_round_rate().
> > In that case for quite some modes we'll be getting -EINVAL and no video
> > output at all.
> > 
> > But given there's some tolerance to real pixel clock in TVs/monitors
> > we may still give it a try with the clock as close to requested one as
> > PLL on the board may generate. So we just do a fixup to what current
> > board may provide.
> > 
> > Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
> > Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> > Cc: David Airlie <airlied@...ux.ie>
> > Cc: Jose Abreu <joabreu@...opsys.com>
> > ---
> >  drivers/gpu/drm/arc/arcpgu_crtc.c | 16 +++++++---------
> >  1 file changed, 7 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/arc/arcpgu_crtc.c b/drivers/gpu/drm/arc/arcpgu_crtc.c
> > index ad9a95916f1f..3f2823c1efc3 100644
> > --- a/drivers/gpu/drm/arc/arcpgu_crtc.c
> > +++ b/drivers/gpu/drm/arc/arcpgu_crtc.c
> > @@ -129,18 +129,16 @@ static void arc_pgu_crtc_disable(struct drm_crtc *crtc)
> >  			      ~ARCPGU_CTRL_ENABLE_MASK);
> >  }
> >  
> > -static int arc_pgu_crtc_atomic_check(struct drm_crtc *crtc,
> > -				     struct drm_crtc_state *state)
> > +static bool arc_pgu_crtc_mode_fixup(struct drm_crtc *crtc,
> > +				    const struct drm_display_mode *mode,
> > +				    struct drm_display_mode *adjusted_mode)
> 
> This isn't required at all, see drm_crtc_state.adjusted_mode. Just update
> that and you're good - .mode_fixup is the backwards compatibility function
> for old kms drivers, atomic_check is strictly more powerful.

So if I understood you correct here what I really need is just to get rid of existing check,
right? I.e. the following is to be in v2 respin:
------------------------------->8-------------------------------
diff --git a/drivers/gpu/drm/arc/arcpgu_crtc.c b/drivers/gpu/drm/arc/arcpgu_crtc.c
index ad9a95916f1f..86f1555914e8 100644
--- a/drivers/gpu/drm/arc/arcpgu_crtc.c
+++ b/drivers/gpu/drm/arc/arcpgu_crtc.c
@@ -129,20 +129,6 @@ static void arc_pgu_crtc_disable(struct drm_crtc *crtc)
                              ~ARCPGU_CTRL_ENABLE_MASK);
 }
 
-static int arc_pgu_crtc_atomic_check(struct drm_crtc *crtc,
-                                    struct drm_crtc_state *state)
-{
-       struct arcpgu_drm_private *arcpgu = crtc_to_arcpgu_priv(crtc);
-       struct drm_display_mode *mode = &state->adjusted_mode;
-       long rate, clk_rate = mode->clock * 1000;
-
-       rate = clk_round_rate(arcpgu->clk, clk_rate);
-       if (rate != clk_rate)
-               return -EINVAL;
-
-       return 0;
-}
-
 static void arc_pgu_crtc_atomic_begin(struct drm_crtc *crtc,
                                      struct drm_crtc_state *state)
 {
@@ -165,7 +151,6 @@ static const struct drm_crtc_helper_funcs arc_pgu_crtc_helper_funcs = {
        .disable        = arc_pgu_crtc_disable,
        .prepare        = arc_pgu_crtc_disable,
        .commit         = arc_pgu_crtc_enable,
-       .atomic_check   = arc_pgu_crtc_atomic_check,
        .atomic_begin   = arc_pgu_crtc_atomic_begin,
 };
------------------------------->8-------------------------------

> Please also make sure the documentation properly explains this, and if
> not, please submit a patch to improve it.

You mean explains what? That .mode_fixup is not meant to be used in
new code?

-Alexey