linux-kernel - Re: [PATCH v4 1/4] usb: gadget: Support already-mapped DMA SGs

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Message-ID: <ZaruU5BpQF8SeZZS@lizhi-Precision-Tower-5810>
Date: Fri, 19 Jan 2024 16:49:07 -0500
From: Frank Li <Frank.li@....com>
To: Paul Cercueil <paul@...pouillou.net>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jonathan Corbet <corbet@....net>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Jonathan Cameron <jic23@...nel.org>,
	Nuno Sá <noname.nuno@...il.com>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	linux-usb@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v4 1/4] usb: gadget: Support already-mapped DMA SGs

On Wed, Jan 17, 2024 at 01:26:43PM +0100, Paul Cercueil wrote:
> Add a new 'sg_was_mapped' field to the struct usb_request. This field
> can be used to indicate that the scatterlist associated to the USB
> transfer has already been mapped into the DMA space, and it does not
> have to be done internally.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/usb/gadget/udc/core.c | 7 ++++++-
>  include/linux/usb/gadget.h    | 2 ++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index d59f94464b87..9d4150124fdb 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c
> @@ -903,6 +903,11 @@ int usb_gadget_map_request_by_dev(struct device *dev,
>  	if (req->length == 0)
>  		return 0;
>  
> +	if (req->sg_was_mapped) {
> +		req->num_mapped_sgs = req->num_sgs;
> +		return 0;
> +	}
> +
>  	if (req->num_sgs) {
>  		int     mapped;
>  
> @@ -948,7 +953,7 @@ EXPORT_SYMBOL_GPL(usb_gadget_map_request);
>  void usb_gadget_unmap_request_by_dev(struct device *dev,
>  		struct usb_request *req, int is_in)
>  {
> -	if (req->length == 0)
> +	if (req->length == 0 || req->sg_was_mapped)
>  		return;
>  
>  	if (req->num_mapped_sgs) {
> diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
> index a771ccc038ac..c529e4e06997 100644
> --- a/include/linux/usb/gadget.h
> +++ b/include/linux/usb/gadget.h
> @@ -52,6 +52,7 @@ struct usb_ep;
>   * @short_not_ok: When reading data, makes short packets be
>   *     treated as errors (queue stops advancing till cleanup).
>   * @dma_mapped: Indicates if request has been mapped to DMA (internal)
> + * @sg_was_mapped: Set if the scatterlist has been mapped before the request
>   * @complete: Function called when request completes, so this request and
>   *	its buffer may be re-used.  The function will always be called with
>   *	interrupts disabled, and it must not sleep.
> @@ -111,6 +112,7 @@ struct usb_request {
>  	unsigned		zero:1;
>  	unsigned		short_not_ok:1;
>  	unsigned		dma_mapped:1;
> +	unsigned		sg_was_mapped:1;

why not use dma_mapped direclty?

Frank

>  
>  	void			(*complete)(struct usb_ep *ep,
>  					struct usb_request *req);
> -- 
> 2.43.0
>