linux-kernel - Re: [PATCH 3/3] drm: omapdrm: Do no allocate non-scanout GEMs through DMM/TILER

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Message-Id: <4B3F8E50-3472-4AED-9A77-3E265DF8C928@goldelico.com>
Date:   Sun, 30 Oct 2022 23:08:52 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Cc:     tomba@...nel.org, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, merlijn@...zup.org, tony@...mide.com
Subject: Re: [PATCH 3/3] drm: omapdrm: Do no allocate non-scanout GEMs through
 DMM/TILER

Hi Ivaylo,

it took a while until I found time to test newer kernels (mainline + Letux additions)
on the OMAP5 Pyra but unfortunately I did not get screen display for v6.1. Even worse,
the console was flooded by

[   39.419846] WARNING: CPU: 0 PID: 3673 at drivers/bus/omap_l3_noc.c:139 l3_interrupt_handler+0x23c/0x330
[   39.429914] 44000000.l3-noc:L3 Custom Error: MASTER MPU TARGET GPMC (Idle): Data Access in Supervisor mode during Functional access
...

making the system unuseable.

After doing some manual bisect by installing different kernel versions on the boot SD card,
I was able to identify that it crept in between v5.18 and v5.19-rc1. A git bisect on this
range (adding Letux patches on top of each bisect base) did reveal this patch as the first bad one.

After reverting it seems as if I can use any v5.19 .. v6.1-rc2 kernel without issues.

Now I wonder why this patch breaks my system?

BR and thanks,
Nikolaus


> Am 19.01.2022 um 11:23 schrieb Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>:
> 
> On devices with DMM, all allocations are done through either DMM or TILER.
> DMM/TILER being a limited resource means that such allocations will start
> to fail before actual free memory is exhausted. What is even worse is that
> with time DMM/TILER space gets fragmented to the point that even if we have
> enough free DMM/TILER space and free memory, allocation fails because there
> is no big enough free block in DMM/TILER space.
> 
> Such failures can be easily observed with OMAP xorg DDX, for example -
> starting few GUI applications (so buffers for their windows are allocated)
> and then rotating landscape<->portrait while closing and opening new
> windows soon results in allocation failures.
> 
> Fix that by mapping buffers through DMM/TILER only when really needed,
> like, for scanout buffers.
> 
> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> ---
> drivers/gpu/drm/omapdrm/omap_gem.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
> index 41c1a6d..cf57179 100644
> --- a/drivers/gpu/drm/omapdrm/omap_gem.c
> +++ b/drivers/gpu/drm/omapdrm/omap_gem.c
> @@ -821,10 +821,12 @@ int omap_gem_pin(struct drm_gem_object *obj, dma_addr_t *dma_addr)
> 			if (ret)
> 				goto fail;
> 
> -			if (priv->has_dmm) {
> -				ret = omap_gem_pin_tiler(obj);
> -				if (ret)
> -					goto fail;
> +			if (omap_obj->flags & OMAP_BO_SCANOUT) {
> +				if (priv->has_dmm) {
> +					ret = omap_gem_pin_tiler(obj);
> +					if (ret)
> +						goto fail;
> +				}
> 			}
> 		} else {
> 			refcount_inc(&omap_obj->pin_cnt);
> @@ -861,6 +863,8 @@ static void omap_gem_unpin_locked(struct drm_gem_object *obj)
> 			kfree(omap_obj->sgt);
> 			omap_obj->sgt = NULL;
> 		}
> +		if (!(omap_obj->flags & OMAP_BO_SCANOUT))
> +			return;
> 		if (priv->has_dmm) {
> 			ret = tiler_unpin(omap_obj->block);
> 			if (ret) {
> -- 
> 1.9.1
>