linux-kernel - Re: [PATCH 8/8] drm/tidss: Enable Dual and Duplicate Modes for OLDI

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Date:   Thu, 28 Jul 2022 09:46:16 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Aradhya Bhatia <a-bhatia1@...com>
Cc:     Darren Etheridge <detheridge@...com>, Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rahul T R <r-ravikumar@...com>,
        Krunal Bhargav <k-bhargav@...com>,
        Devarsh Thakkar <devarsht@...com>,
        DRI Development List <dri-devel@...ts.freedesktop.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jyri Sarha <jyri.sarha@....fi>
Subject: Re: [PATCH 8/8] drm/tidss: Enable Dual and Duplicate Modes for OLDI

On 27/07/2022 16:22, Tomi Valkeinen wrote:
> Hi,
> 
> On 19/07/2022 11:08, Aradhya Bhatia wrote:
>> The AM625 DSS peripheral supports 2 OLDI TXes which can work to enable 2
>> duplicated displays of smaller resolutions or enable a single Dual-Link
>> display with a higher resolution (1920x1200).
>>
>> Configure the necessary register to enable the different modes.
>>
>> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
>> ---
>>   drivers/gpu/drm/tidss/tidss_dispc.c | 44 +++++++++++++++++++++++++++--
>>   1 file changed, 41 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c 
>> b/drivers/gpu/drm/tidss/tidss_dispc.c
>> index 0b9689453ee8..28cb61259471 100644
>> --- a/drivers/gpu/drm/tidss/tidss_dispc.c
>> +++ b/drivers/gpu/drm/tidss/tidss_dispc.c
>> @@ -1021,8 +1021,8 @@ static void dispc_enable_oldi(struct 
>> dispc_device *dispc, u32 hw_videoport,
>>       int count = 0;
>>       /*
>> -     * For the moment DUALMODESYNC, MASTERSLAVE, MODE, and SRC
>> -     * bits of DISPC_VP_DSS_OLDI_CFG are set statically to 0.
>> +     * For the moment MASTERSLAVE, and SRC bits of 
>> DISPC_VP_DSS_OLDI_CFG are
>> +     * set statically to 0.
>>        */
>>       if (fmt->data_width == 24)
>> @@ -1039,7 +1039,45 @@ static void dispc_enable_oldi(struct 
>> dispc_device *dispc, u32 hw_videoport,
>>       oldi_cfg |= BIT(0); /* ENABLE */
>> -    dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, 
>> oldi_cfg);
>> +    /*
>> +     * As per all the current implementations of DSS, the OLDI TXes 
>> are present only on
>> +     * hw_videoport = 0 (OLDI TX 0). However, the config register for 
>> 2nd OLDI TX (OLDI TX 1)
>> +     * is present in the address space of hw_videoport = 1. Hence, 
>> using "hw_videoport + 1" to
>> +     * configure OLDI TX 1.
>> +     */
>> +
>> +    switch (dispc->oldi_mode) {
>> +    case OLDI_MODE_OFF:
>> +        oldi_cfg &= ~BIT(0); /* DISABLE */
>> +        dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, 
>> oldi_cfg);
>> +        dispc_vp_write(dispc, hw_videoport + 1, 
>> DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
>> +        break;
>> +
>> +    case OLDI_SINGLE_LINK_SINGLE_MODE_0:
>> +        dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, 
>> oldi_cfg);
>> +        break;
>> +
>> +    case OLDI_SINGLE_LINK_SINGLE_MODE_1:
>> +        dispc_vp_write(dispc, hw_videoport + 1, 
>> DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
>> +        break;
>> +
>> +    case OLDI_SINGLE_LINK_DUPLICATE_MODE:
>> +        oldi_cfg |= BIT(5); /* DUPLICATE MODE */
>> +        dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, 
>> oldi_cfg);
>> +        dispc_vp_write(dispc, hw_videoport + 1, 
>> DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
>> +        break;
>> +
>> +    case OLDI_DUAL_LINK:
>> +        oldi_cfg |= BIT(11); /* DUALMODESYNC */
>> +        dispc_vp_write(dispc, hw_videoport, DISPC_VP_DSS_OLDI_CFG, 
>> oldi_cfg);
>> +        dispc_vp_write(dispc, hw_videoport + 1, 
>> DISPC_VP_DSS_OLDI_CFG, oldi_cfg);
>> +        break;
>> +
>> +    default:
>> +        dev_warn(dispc->dev, "%s: Incorrect oldi mode. Returning.\n",
>> +             __func__);
>> +        return;
>> +    }
>>       while (!(oldi_reset_bit & dispc_read(dispc, DSS_SYSSTATUS)) &&
>>              count < 10000)
> 
> This feels a bit hacky:
> 
> - The function is dispc_enable_oldi, but the above code also disables 
> oldi. We have code in dispc_vp_unprepare() which disables OLDI at the 
> moment.
> 
> - The function takes hw_videoport as a parameter, and is designed to 
> work on that videoport. The above operates on two videoports. Isn't the 
> function also called for hw_videoport +1, which would result in reg 
> writes to hw_videoport + 2?
> 
> - No matching code in dispc_vp_unprepare
> 
> Obviously the duplicate mode (I presume that's "cloning") and the dual 
> link complicate things here, and I have to say I haven't worked with 
> such setups. But I think somehow this should be restructured so that 
> common configuration (common to the OLDIs) is done somewhere else.
> 
> I would guess that there are other drivers that support cloning and dual 
> mode. Did you have a look how they handle things?

Oh, I see now... There's just one dss video port for OLDI, the same as 
in am65x, but that single video port is now connected to two OLDI TXes. 
And thus this function will only be called for the single video port.

But... The registers for the second OLDI are part of the second video 
port (DPI) register block?

  Tomi