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Date:   Tue, 25 Oct 2022 21:38:12 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Ricardo Ribalda <ribalda@chromium.org>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org, Guenter Roeck <linux@roeck-us.net>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/1] media: uvcvideo: Handle errors from calls to
 usb_string
Message-ID: <Y1gtFNPYmegewAGH@pendragon.ideasonboard.com>
References: <20221025-usb-string-v1-0-4c351b6907bb@chromium.org>
 <20221025-usb-string-v1-1-4c351b6907bb@chromium.org>
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In-Reply-To: <20221025-usb-string-v1-1-4c351b6907bb@chromium.org>
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Hi Ricardo and Guenter,

Thank you for the patch.

On Tue, Oct 25, 2022 at 04:41:01PM +0200, Ricardo Ribalda wrote:
> From: Guenter Roeck <linux@roeck-us.net>
> 
> On a Webcam from Quanta, we see the following error.
> 
> usb 3-5: New USB device found, idVendor=0408, idProduct=30d2, bcdDevice= 0.03
> usb 3-5: New USB device strings: Mfr=3, Product=1, SerialNumber=2
> usb 3-5: Product: USB2.0 HD UVC WebCam
> usb 3-5: Manufacturer: Quanta
> usb 3-5: SerialNumber: 0x0001
> ...
> uvcvideo: Found UVC 1.10 device USB2.0 HD UVC WebCam (0408:30d2)
> uvcvideo: Failed to initialize entity for entity 5
> uvcvideo: Failed to register entities (-22).
> 
> The Webcam reports an entity of type UVC_VC_EXTENSION_UNIT. It reports a
> string index of '7' associated with that entity. The attempt to read that
> string from the camera fails with error -32 (-EPIPE). usb_string() returns
> that error, but it is ignored. As result, the entity name is empty. This
> later causes v4l2_device_register_subdev() to return -EINVAL, and no
> entities are registered as result.
> 
> While this appears to be a firmware problem with the camera, the kernel
> should still handle the situation gracefully. To do that, check the return
> value from usb_string(). If it reports an error, assign the entity's
> default name.

Sounds good. The perfect world in which firmwares could be fixed doesn't
exist.

> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index 215fb483efb0..828c443faaa9 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -879,10 +879,8 @@ static int uvc_parse_vendor_control(struct uvc_device *dev,
>  					       + n;
>  		memcpy(unit->extension.bmControls, &buffer[23+p], 2*n);
>  
> -		if (buffer[24+p+2*n] != 0)
> -			usb_string(udev, buffer[24+p+2*n], unit->name,
> -				   sizeof(unit->name));
> -		else
> +		if (buffer[24+p+2*n] == 0 ||
> +		    usb_string(udev, buffer[24+p+2*n], unit->name, sizeof(unit->name)) < 0)
>  			sprintf(unit->name, "Extension %u", buffer[3]);

There's quite a bit of common code between all the cases. I'll submit a
patch that refactors it on top. There's thus no need for nitpicking
here, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

>  
>  		list_add_tail(&unit->list, &dev->entities);
> @@ -1006,15 +1004,15 @@ static int uvc_parse_standard_control(struct uvc_device *dev,
>  			memcpy(term->media.bmTransportModes, &buffer[10+n], p);
>  		}
>  
> -		if (buffer[7] != 0)
> -			usb_string(udev, buffer[7], term->name,
> -				   sizeof(term->name));
> -		else if (UVC_ENTITY_TYPE(term) == UVC_ITT_CAMERA)
> -			sprintf(term->name, "Camera %u", buffer[3]);
> -		else if (UVC_ENTITY_TYPE(term) == UVC_ITT_MEDIA_TRANSPORT_INPUT)
> -			sprintf(term->name, "Media %u", buffer[3]);
> -		else
> -			sprintf(term->name, "Input %u", buffer[3]);
> +		if (buffer[7] == 0 ||
> +		    usb_string(udev, buffer[7], term->name, sizeof(term->name)) < 0) {
> +			if (UVC_ENTITY_TYPE(term) == UVC_ITT_CAMERA)
> +				sprintf(term->name, "Camera %u", buffer[3]);
> +			if (UVC_ENTITY_TYPE(term) == UVC_ITT_MEDIA_TRANSPORT_INPUT)
> +				sprintf(term->name, "Media %u", buffer[3]);
> +			else
> +				sprintf(term->name, "Input %u", buffer[3]);
> +		}
>  
>  		list_add_tail(&term->list, &dev->entities);
>  		break;
> @@ -1047,10 +1045,8 @@ static int uvc_parse_standard_control(struct uvc_device *dev,
>  
>  		memcpy(term->baSourceID, &buffer[7], 1);
>  
> -		if (buffer[8] != 0)
> -			usb_string(udev, buffer[8], term->name,
> -				   sizeof(term->name));
> -		else
> +		if (buffer[8] == 0 ||
> +		    usb_string(udev, buffer[8], term->name, sizeof(term->name)) < 0)
>  			sprintf(term->name, "Output %u", buffer[3]);
>  
>  		list_add_tail(&term->list, &dev->entities);
> @@ -1072,10 +1068,8 @@ static int uvc_parse_standard_control(struct uvc_device *dev,
>  
>  		memcpy(unit->baSourceID, &buffer[5], p);
>  
> -		if (buffer[5+p] != 0)
> -			usb_string(udev, buffer[5+p], unit->name,
> -				   sizeof(unit->name));
> -		else
> +		if (buffer[5+p] == 0 ||
> +		    usb_string(udev, buffer[5+p], unit->name, sizeof(unit->name)) < 0)
>  			sprintf(unit->name, "Selector %u", buffer[3]);
>  
>  		list_add_tail(&unit->list, &dev->entities);
> @@ -1105,10 +1099,8 @@ static int uvc_parse_standard_control(struct uvc_device *dev,
>  		if (dev->uvc_version >= 0x0110)
>  			unit->processing.bmVideoStandards = buffer[9+n];
>  
> -		if (buffer[8+n] != 0)
> -			usb_string(udev, buffer[8+n], unit->name,
> -				   sizeof(unit->name));
> -		else
> +		if (buffer[8+n] == 0 ||
> +		    usb_string(udev, buffer[8+n], unit->name, sizeof(unit->name)) < 0)
>  			sprintf(unit->name, "Processing %u", buffer[3]);
>  
>  		list_add_tail(&unit->list, &dev->entities);
> @@ -1136,10 +1128,8 @@ static int uvc_parse_standard_control(struct uvc_device *dev,
>  		unit->extension.bmControls = (u8 *)unit + sizeof(*unit);
>  		memcpy(unit->extension.bmControls, &buffer[23+p], n);
>  
> -		if (buffer[23+p+n] != 0)
> -			usb_string(udev, buffer[23+p+n], unit->name,
> -				   sizeof(unit->name));
> -		else
> +		if (buffer[23+p+n] == 0 ||
> +		    usb_string(udev, buffer[23+p+n], unit->name, sizeof(unit->name)) < 0)
>  			sprintf(unit->name, "Extension %u", buffer[3]);
>  
>  		list_add_tail(&unit->list, &dev->entities);
> 

-- 
Regards,

Laurent Pinchart