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

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Message-ID: <Zaspld3SOwDftYhj@lizhi-Precision-Tower-5810>
Date: Fri, 19 Jan 2024 21:01:57 -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 Sat, Jan 20, 2024 at 01:14:52AM +0100, Paul Cercueil wrote:
> Hi Frank,
> 
> Le vendredi 19 janvier 2024 à 16:49 -0500, Frank Li a écrit :
> > 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?
> 
> Because of the unmap case. We want to know whether we should unmap or
> not.

I see, Thanks
Frank

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