linux-kernel - Re: [PATCH] drm/panthor: Simplify FW fast reset path

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Message-ID: <20241119101612.351c6302@collabora.com>
Date: Tue, 19 Nov 2024 10:16:12 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Karunika Choo <karunika.choo@....com>
Cc: nd@....com, Steven Price <steven.price@....com>, Liviu Dudau
 <liviu.dudau@....com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panthor: Simplify FW fast reset path

On Mon, 18 Nov 2024 15:21:52 +0000
Karunika Choo <karunika.choo@....com> wrote:

> Stop checking the FW halt_status as MCU_STATUS should be sufficient.
> This should make the check for successful FW halt and subsequently
> setting fast_reset to true more robust.
> 
> We should also clear GLB_REQ.GLB_HALT bit only on post-reset prior
> to starting the FW.

And maybe add 'only if we're doing a fast reset, because the slow reset
will re-initialize all FW sections, including the global interface.'

> 
> Signed-off-by: Karunika Choo <karunika.choo@....com>
> ---
>  drivers/gpu/drm/panthor/panthor_fw.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
> index ecca5565ce41..6d41089b84ab 100644
> --- a/drivers/gpu/drm/panthor/panthor_fw.c
> +++ b/drivers/gpu/drm/panthor/panthor_fw.c
> @@ -1098,17 +1098,11 @@ void panthor_fw_pre_reset(struct panthor_device *ptdev, bool on_hang)
>  		panthor_fw_update_reqs(glb_iface, req, GLB_HALT, GLB_HALT);
>  		gpu_write(ptdev, CSF_DOORBELL(CSF_GLB_DOORBELL_ID), 1);
>  		if (!readl_poll_timeout(ptdev->iomem + MCU_STATUS, status,
> -					status == MCU_STATUS_HALT, 10, 100000) &&
> -		    glb_iface->output->halt_status == PANTHOR_FW_HALT_OK) {
> +					status == MCU_STATUS_HALT, 10, 100000)) {
>  			ptdev->fw->fast_reset = true;
>  		} else {
>  			drm_warn(&ptdev->base, "Failed to cleanly suspend MCU");
>  		}
> -
> -		/* The FW detects 0 -> 1 transitions. Make sure we reset
> -		 * the HALT bit before the FW is rebooted.
> -		 */
> -		panthor_fw_update_reqs(glb_iface, req, 0, GLB_HALT);
>  	}
>  
>  	panthor_job_irq_suspend(&ptdev->fw->irq);
> @@ -1134,6 +1128,11 @@ int panthor_fw_post_reset(struct panthor_device *ptdev)
>  	 * the FW sections. If it fails, go for a full reset.
>  	 */
>  	if (ptdev->fw->fast_reset) {
> +		/* The FW detects 0 -> 1 transitions. Make sure we reset
> +		 * the HALT bit before the FW is rebooted.

Can you add
                 * This is not needed on a slow reset, because FW
                 * sections are re-initialized.

?

> +		 */
> +		panthor_fw_update_reqs(glb_iface, req, 0, GLB_HALT);
> +
>  		ret = panthor_fw_start(ptdev);
>  		if (!ret)
>  			goto out;

This these 2 minor nits addressed, the patch is

`Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>`