linux-kernel - Re: [RFC/RFT PATCH 1/6] uvcvideo: Refactor URB descriptors

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Date:   Sat, 6 Jan 2018 18:30:42 +0000
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        laurent.pinchart@...asonboard.com,
        Olivier BRAUN <olivier.braun@...reolabs.com>,
        kieran.bingham@...asonboard.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jaejoong Kim <climbbb.kim@...il.com>,
        Baoyou Xie <baoyou.xie@...aro.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Aviv Greenberg <avivgr@...il.com>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Patrick Johnson <teknotus@...not.us>,
        Jim Lin <jilin@...dia.com>
Subject: Re: [RFC/RFT PATCH 1/6] uvcvideo: Refactor URB descriptors

Hi Guennadi,

Thanks for your review,

On 04/01/18 18:24, Guennadi Liakhovetski wrote:
> Hi Kieran,
> 
> Just minor suggestions below:
> 
> On Wed, 3 Jan 2018, Kieran Bingham wrote:
> 
>> From: Kieran Bingham <kieran.bingham@...asonboard.com>
>>
>> We currently store three separate arrays for each URB reference we hold.
>>
>> Objectify the data needed to track URBs into a single uvc_urb structure,
>> allowing better object management and tracking of the URB.
>>
>> All accesses to the data pointers through stream, are converted to use a
>> uvc_urb pointer for consistency.
>>
>> Signed-off-by: Kieran Bingham <kieran.bingham@...asonboard.com>
>> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>> ---
>>  drivers/media/usb/uvc/uvc_video.c | 46 ++++++++++++++++++++------------
>>  drivers/media/usb/uvc/uvcvideo.h  | 18 ++++++++++---
>>  2 files changed, 44 insertions(+), 20 deletions(-)
> 
> [snip]
> 
>> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
>> index 19e725e2bda5..4afa8ce13ea7 100644
>> --- a/drivers/media/usb/uvc/uvcvideo.h
>> +++ b/drivers/media/usb/uvc/uvcvideo.h
>> @@ -479,6 +479,20 @@ struct uvc_stats_stream {
>>  	unsigned int max_sof;		/* Maximum STC.SOF value */
>>  };
>>  
>> +/**
>> + * struct uvc_urb - URB context management structure
>> + *
>> + * @urb: described URB. Must be allocated with usb_alloc_urb()
> 
> Didn't you mean "describes?"

Hrm ... I think I meant described as in "This is the URB described by this
uvc_urb structure", rather than "this variable describes the URB"

Perhaps I'll change this to:

  @urb: The URB described by this context structure.

I think the 'must be allocated with usb_alloc_urb() is fairly implicit, so could
be dropped in that case.

> 
>> + * @urb_buffer: memory storage for the URB
>> + * @urb_dma: DMA coherent addressing for the urb_buffer
> 
> The whole struct describes URBs, so, I wouldn't repeat that in these two 
> field names, I'd just call them "buffer" and "dma." OTOH, later you add 
> more fields like "stream," which aren't per-URB, so, maybe you want to 
> keep these prefixes.

These names were kept from the original fields. But actually I think you're
right here - it wouldn't hurt to shorten the names, even with the other fields
added.

> Thanks
> Guennadi
> 
>> + */
>> +struct uvc_urb {
>> +	struct urb *urb;
>> +
>> +	char *urb_buffer;
>> +	dma_addr_t urb_dma;
>> +};
>> +
>>  struct uvc_streaming {
>>  	struct list_head list;
>>  	struct uvc_device *dev;
>> @@ -521,9 +535,7 @@ struct uvc_streaming {
>>  		__u32 max_payload_size;
>>  	} bulk;
>>  
>> -	struct urb *urb[UVC_URBS];
>> -	char *urb_buffer[UVC_URBS];
>> -	dma_addr_t urb_dma[UVC_URBS];
>> +	struct uvc_urb uvc_urb[UVC_URBS];
>>  	unsigned int urb_size;
>>  
>>  	__u32 sequence;
>> -- 
>> git-series 0.9.1
>>

--
Kieran