Re: [PATCH] drm: hdlcd: allow HDLCD to be used without interrupt

[Liviu Dudau <liviu.dudau-5wv7dgnIgG8@public.gmane.org>]

On Fri, Jul 28, 2017 at 04:58:27PM +0100, Russell King - ARM Linux wrote:
> On Fri, Jul 28, 2017 at 04:23:11PM +0100, Liviu Dudau wrote:
> > On Wed, Jul 26, 2017 at 11:27:48AM +0100, Russell King - ARM Linux wrote:
> > > On Wed, Jul 26, 2017 at 11:05:39AM +0100, Russell King wrote:
> > > > Some ARM platforms do not wire the HDLCD interrupt.  Allow hdlcd to
> > > > initialise without an interrupt present.
> > > > 
> > > > Signed-off-by: Russell King <rmk+kernel-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org>
> > > 
> > 
> > Hi Russell,
> > 
> > Sorry for my silence, I was on holiday this week and just came back
> > today.
> > 
> > > This isn't fully functional on ARM MPS platforms yet, but at least
> > > gets us further.  Without any display connected:
> > > 
> > > [   14.315986] [drm] found ARM HDLCD version r0p0
> > > [   14.557038] tda998x 2-0070: found TDA19988
> > > [   14.622232] hdlcd 40205000.hdlcd: bound 2-0070 (ops 0x213534)
> > > [   14.630406] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
> > > [   14.639335] [drm] No driver support for vblank timestamp query.
> > > [   14.653210] [drm] Cannot find any crtc or sizes - going 1024x768
> > > [   15.232556] hdlcd 40205000.hdlcd: fb0:  frame buffer device
> > > [   15.284076] [drm] Initialized hdlcd 1.0.0 20151021 for 40205000.hdlcd on minor 0
> > > 
> > > With a TV connected, the driver doesn't initialise:
> > > 
> > > [   14.422810] [drm] found ARM HDLCD version r0p0
> > > [   14.657227] tda998x 2-0070: found TDA19988
> > > [   14.722439] hdlcd 40205000.hdlcd: bound 2-0070 (ops 0x213534)
> > > [   14.730613] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
> > > [   14.739538] [drm] No driver support for vblank timestamp query.
> > > [   15.311977] hdlcd 40205000.hdlcd: Failed to set initial hw configuration.
> > > [   15.357402] hdlcd 40205000.hdlcd: master bind failed: -12
> > > [   15.365082] tda998x: probe of 2-0070 failed with error -12
> > > 
> > > I don't think this is correct behaviour - if we fail to set an initial
> > > configuration (which will be based on the resolution of the connected
> > > display) why should the driver fail to probe - it's not that there is
> > > no device, it's (in this case) that there aren't the resources for the
> > > chosen mode.  Userspace could always try setting a different mode.
> > > 
> > > I suspect the above failure is down to either (a) not having enough
> > > memory available to allocate a 1920x1080 frame buffer, or (b) not
> > > (yet) being able to program the hdlcd pixel clock for this platform,
> > > which is currently hard-coded in DT at 23.75MHz.
> > 
> > I don't think it is the clock, if that fails then you would not see the
> > r0p0 version number being printed. Due to the fact that until now HDLCD
> > has run mostly on platforms that have SCP, which takes care of actual
> > setup of the clocks, it is pretty lax on errors on pixel clock setup.
> 
> Note, however, that in this case, the clock is a fixed frequency clock.
> I wasn't meaning a failure to obtain the clock, I was meaning a failure
> to set the appropriate rate.

Yeah, we both meant the same thing. :) HDLCD is not checking that
strictly that the appropriate rate was set, although looking into
hdlcd_crtc_atomic_check() we do return -EINVAL if the set rate differs
from what the mode wants. Maybe add a printk there to see if you hit
that case?

> 
> > Also, may I ask what MPS platform you are trying to use? I might be able
> > to source one internally and try to reproduce your problems.
> 
> I'll point you in the direction of Ian Rickards in ARM for that
> information.  (I'm not sure if I can mention the board publically
> yet as its early days...)

Thanks, I'll get in touch with Ian.

Best regards,
Liviu

> 
> -- 
> RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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-- 
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