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

From: vladimir.murzin@arm.com (Vladimir Murzin)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] drm: hdlcd: allow HDLCD to be used without interrupt
Date: Mon, 21 Aug 2017 15:45:21 +0100	[thread overview]
Message-ID: <9cdccb9c-83c5-5867-06a5-3b344102d232@arm.com> (raw)
In-Reply-To: <e68186a4-2435-a969-7eff-21556d6a6b03@arm.com>

On 10/08/17 13:15, Vladimir Murzin wrote:
> On 26/07/17 11:27, Russell King - ARM Linux wrote:
>> 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.
> 
> Given it is NOMMU it is likely (a). Usually, tweaking FORCE_MAX_ZONEORDER
> helped me in such cases.

Ok, with CONFIG_FORCE_MAX_ZONEORDER=12 I see

[    5.242423] [drm] found ARM HDLCD version r0p0
[    5.493835] tda998x 2-0070: found TDA19988
[    5.527771] hdlcd 40205000.hdlcd: bound 2-0070 (ops 0x1470f8)
[    5.535819] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[    5.543478] [drm] No driver support for vblank timestamp query.
[    7.443189] hdlcd 40205000.hdlcd: fb0:  frame buffer device
[    7.501975] [drm] Initialized hdlcd 1.0.0 20151021 for 40205000.hdlcd on minor 0

when display is connected.

To make fb-test [1] happy I had to apply following diff:

diff --git a/drivers/gpu/drm/arm/Kconfig b/drivers/gpu/drm/arm/Kconfig
index 9a18e1b..d4cb1b1 100644
--- a/drivers/gpu/drm/arm/Kconfig
+++ b/drivers/gpu/drm/arm/Kconfig
@@ -10,6 +10,7 @@ config DRM_HDLCD
        select DRM_ARM
        select DRM_KMS_HELPER
        select DRM_KMS_CMA_HELPER
+       select FB_PROVIDE_GET_FB_UNMAPPED_AREA if !MMU
        help
          Choose this option if you have an ARM High Definition Colour LCD
          controller.

(The only user of FB_PROVIDE_GET_FB_UNMAPPED_AREA is NOMMU only drivers/gpu/drm/stm/)

However, I do not see anything on the screen. I'm probably missing something
obvious, so if you have an idea, please let me know and I can test the patch.

[1] https://github.com/prpplague/fb-test-app.git 

Thanks
Vladimir

> 
> Cheers
> Vladimir
> 
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