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

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Date: Sat, 20 Jan 2024 01:14:52 +0100
From: Paul Cercueil <paul@...pouillou.net>
To: Frank Li <Frank.li@....com>
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

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.

> 
> Frank

Cheers,
-Paul

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