linux-kernel - Re: [RESEND RFC PATCH 0/7] sun8i H3 HDMI glue driver for DW HDMI

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Date:   Thu, 21 Sep 2017 11:59:27 +0200
From:   Hans Verkuil <hansverk@...co.com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        maxime.ripard@...e-electrons.com, wens@...e.org
Cc:     Laurent.pinchart@...asonboard.com, hans.verkuil@...co.com,
        narmstrong@...libre.com, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        icenowy@...c.io, linux-sunxi@...glegroups.com,
        linux-media@...r.kernel.org
Subject: Re: [RESEND RFC PATCH 0/7] sun8i H3 HDMI glue driver for DW HDMI

On 09/21/17 11:39, Jose Abreu wrote:
> Hi Jernej,
> 
> On 20-09-2017 21:01, Jernej Skrabec wrote:
>> [added media mailing list due to CEC question]
>>
>> This patch series adds a HDMI glue driver for Allwinner H3 SoC. For now, only
>> video and CEC functionality is supported. Audio needs more tweaks.
>>
>> Series is based on the H3 DE2 patch series available on mailing list:
>> https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.infradead.org_pipermail_linux-2Darm-2Dkernel_2017-2DAugust_522697.html&d=DwIBAg&c=DPL6_X_6JkXFx7AXWqB0tg&r=WHDsc6kcWAl4i96Vm5hJ_19IJiuxx_p_Rzo2g-uHDKw&m=coyfcQKSr2asrHcaCeWFmAP_9nkFkRK8s7Uw5bmVei4&s=JCFaMXK1MmZ3jE745_YcqZhZkaqtc6UapGfSSapcz_s&e= 
>> (ignore patches marked with [NOT FOR REVIEW NOW] tag)
>>
>> Patch 1 adds support for polling plug detection since custom PHY used here
>> doesn't support HPD interrupt.
>>
>> Patch 2 enables overflow workaround for v1.32a. This HDMI controller exhibits
>> same issues as HDMI controller used in iMX6 SoCs.
>>
>> Patch 3 adds CLK_SET_RATE_PARENT to hdmi clock.
>>
>> Patch 4 adds dt bindings documentation.
>>
>> Patch 5 adds actual H3 HDMI glue driver.
>>
>> Patch 6 and 7 add HDMI node to DT and enable it where needed.
>>
>> Allwinner used DW HDMI controller in a non standard way:
>> - register offsets obfuscation layer, which can fortunately be turned off
>> - register read lock, which has to be disabled by magic number
>> - custom PHY, which have to be initialized before DW HDMI controller
>> - non standard clocks
>> - no HPD interrupt
>>
>> Because of that, I have two questions:
>> - Since HPD have to be polled, is it enough just to enable poll mode? I'm
>>   mainly concerned about invalidating CEC address here.
> 
> You mean you get no interrupt when HPD status changes? Hans can
> answer this better but then you will need to invalidate the cec
> physical address yourself because right now its invalidated in
> the dw-hdmi irq handler (see dw_hdmi_irq()).

That's correct. When the HPD goes low you need to call cec_notifier_phys_addr_invalidate()
to invalidate the physical address. This is not terribly time sensitive, i.e.
checking this once a second would be quick enough.

Regards,

	Hans