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SubjectRe: [PATCH 8/8] drm/tidss: Enable Dual and Duplicate Modes for OLDI
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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@ti.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?

Tomi

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