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

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:

quoted

Some ARM platforms do not wire the HDLCD interrupt.  Allow hdlcd to
initialise without an interrupt present.

Signed-off-by: Russell King <redacted>

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.
That is the reason why I have added the 'clocks' entry in debugfs, to be
able to find out the actual clock setup vs what HDLCD would like to have
for the current mode.

If is quite likely to be a memory issue (-12 points that way too).

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.

Best regards,
Liviu

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