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

Paul Cercueil
2024-01-20T00:15:02Z

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@crapouillou.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
> >