linux-kernel - Re: [PATCHv1 03/14] drm/omap: plane: update fifo size on ovl setup

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Message-ID: <34c2588e-7d7e-219f-fd34-9a441d46e0cc@ti.com>
Date:   Fri, 1 Dec 2017 14:10:42 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Sebastian Reichel <sebastian.reichel@...labora.co.uk>,
        Sebastian Reichel <sre@...nel.org>,
        Tony Lindgren <tony@...mide.com>
CC:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-omap@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv1 03/14] drm/omap: plane: update fifo size on ovl setup


On 24/07/17 20:33, Sebastian Reichel wrote:
> This is a workaround for a hardware bug occuring on OMAP3
> with manually updated panels. Details about the HW bug are
> unknown to me, but without this fix the panel refresh does
> not work at all on Nokia N950.
> 
> Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.co.uk>
> ---
>  drivers/gpu/drm/omapdrm/dss/dispc.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
> index fd7504b37e3b..b6dca5ee34d4 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dispc.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
> @@ -1398,6 +1398,18 @@ void dispc_ovl_compute_fifo_thresholds(enum omap_plane_id plane,
>  	}
>  }
>  
> +void dispc_ovl_set_manual_fifo_threshold(enum omap_plane_id plane)
> +{
> +	u32 fifo_low, fifo_high;
> +	bool use_fifo_merge = false;
> +	bool use_manual_update = true;
> +
> +	dispc_ovl_compute_fifo_thresholds(plane, &fifo_low, &fifo_high,
> +					  use_fifo_merge, use_manual_update);
> +
> +	dispc_ovl_set_fifo_threshold(plane, fifo_low, fifo_high);
> +}
> +
>  static void dispc_ovl_set_mflag(enum omap_plane_id plane, bool enable)
>  {
>  	int bit;
> @@ -2566,6 +2578,10 @@ static int dispc_ovl_setup(enum omap_plane_id plane,
>  		oi->zorder, oi->pre_mult_alpha, oi->global_alpha,
>  		oi->rotation_type, replication, vm, mem_to_mem);
>  
> +	/* manual mode needs other fifo thresholds */
> +	if (mgr_fld_read(channel, DISPC_MGR_FLD_STALLMODE))
> +		dispc_ovl_set_manual_fifo_threshold(plane);
> +
>  	return r;
>  }

We don't have the stallmode for all channels. And on OMAP2 it's for
RFBI, and I don't know if that needs different thresholds or not. Also,
I'm not sure if OMAP4-5 DSI needs this. And I think it's good to mention
the unknown bug in the comment too. And yes, it's unknown to me too, I
never figured it out. These thresholds just seemed to work, while the
default did not.

So I think we need to check that the platform is OMAP3 and channel is
LCD. We can later extend that to cover OMAP4-5 if needed.

 Tomi

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