linux-kernel - Re: [PATCH] drm/panthor: Add defer probe for firmware load

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Date: Mon, 15 Apr 2024 09:46:58 +0100
From: Steven Price <steven.price@....com>
To: Andy Yan <andyshrk@....com>, boris.brezillon@...labora.com
Cc: daniel@...ll.ch, airlied@...il.com, liviu.dudau@....com,
 maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 Andy Yan <andy.yan@...k-chips.com>
Subject: Re: [PATCH] drm/panthor: Add defer probe for firmware load

On 13/04/2024 12:49, Andy Yan wrote:
> From: Andy Yan <andy.yan@...k-chips.com>
> 
> The firmware in the rootfs will not be accessible until we
> are in the SYSTEM_RUNNING state, so return EPROBE_DEFER until
> that point.
> This let the driver can load firmware when it is builtin.

The usual solution is that the firmware should be placed in the
initrd/initramfs if the module is included there (or built-in). The same
issue was brought up regarding the powervr driver:

https://lore.kernel.org/dri-devel/20240109120604.603700-1-javierm@redhat.com/T/

I'm not sure if that ever actually reached a conclusion though. The
question was deferred to Greg KH but I didn't see Greg actually getting
involved in the thread.

> Signed-off-by: Andy Yan <andy.yan@...k-chips.com>
> ---
> 
>  drivers/gpu/drm/panthor/panthor_fw.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
> index 33c87a59834e..25e375f8333c 100644
> --- a/drivers/gpu/drm/panthor/panthor_fw.c
> +++ b/drivers/gpu/drm/panthor/panthor_fw.c
> @@ -1336,8 +1336,17 @@ int panthor_fw_init(struct panthor_device *ptdev)
>  	}
>  
>  	ret = panthor_fw_load(ptdev);
> -	if (ret)
> +	if (ret) {
> +		/*
> +		 * The firmware in the rootfs will not be accessible until we
> +		 * are in the SYSTEM_RUNNING state, so return EPROBE_DEFER until
> +		 * that point.
> +		 */
> +		if (system_state < SYSTEM_RUNNING)

This should really only be in the case where ret == -ENOENT - any other
error and the firmware is apparently present but broken in some way, so
there's no point deferring.

I also suspect we'd need some change in panthor_fw_load() to quieten
error messages if we're going to defer on this, in which case it might
make more sense to move this logic into that function.

Steve

> +			ret = -EPROBE_DEFER;
> +
>  		goto err_unplug_fw;
> +	}
>  
>  	ret = panthor_vm_active(fw->vm);
>  	if (ret)