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Subject: Re: [PATCH v4 1/4] usb: gadget: Support already-mapped DMA SGs
From: Paul Cercueil <paul@crapouillou.net>
To: Frank Li <Frank.li@nxp.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jonathan Corbet
 <corbet@lwn.net>, Sumit Semwal <sumit.semwal@linaro.org>, Christian
 =?ISO-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>, Jonathan Cameron
 <jic23@kernel.org>, Nuno =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>,
 Michael Hennerich <Michael.Hennerich@analog.com>, 
 linux-usb@vger.kernel.org, linux-doc@vger.kernel.org, 
 linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, 
 dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org
Date: Sat, 20 Jan 2024 01:14:52 +0100
In-Reply-To: <ZaruU5BpQF8SeZZS@lizhi-Precision-Tower-5810>
References: <20240117122646.41616-1-paul@crapouillou.net>
	 <20240117122646.41616-2-paul@crapouillou.net>
	 <ZaruU5BpQF8SeZZS@lizhi-Precision-Tower-5810>
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Hi Frank,

Le vendredi 19 janvier 2024 =C3=A0 16:49 -0500, Frank Li a =C3=A9crit=C2=A0=
:
> 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.
> >=20
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > ---
> > =C2=A0drivers/usb/gadget/udc/core.c | 7 ++++++-
> > =C2=A0include/linux/usb/gadget.h=C2=A0=C2=A0=C2=A0 | 2 ++
> > =C2=A02 files changed, 8 insertions(+), 1 deletion(-)
> >=20
> > 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,
> > =C2=A0	if (req->length =3D=3D 0)
> > =C2=A0		return 0;
> > =C2=A0
> > +	if (req->sg_was_mapped) {
> > +		req->num_mapped_sgs =3D req->num_sgs;
> > +		return 0;
> > +	}
> > +
> > =C2=A0	if (req->num_sgs) {
> > =C2=A0		int=C2=A0=C2=A0=C2=A0=C2=A0 mapped;
> > =C2=A0
> > @@ -948,7 +953,7 @@ EXPORT_SYMBOL_GPL(usb_gadget_map_request);
> > =C2=A0void usb_gadget_unmap_request_by_dev(struct device *dev,
> > =C2=A0		struct usb_request *req, int is_in)
> > =C2=A0{
> > -	if (req->length =3D=3D 0)
> > +	if (req->length =3D=3D 0 || req->sg_was_mapped)
> > =C2=A0		return;
> > =C2=A0
> > =C2=A0	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;
> > =C2=A0 * @short_not_ok: When reading data, makes short packets be
> > =C2=A0 *=C2=A0=C2=A0=C2=A0=C2=A0 treated as errors (queue stops advanci=
ng till cleanup).
> > =C2=A0 * @dma_mapped: Indicates if request has been mapped to DMA
> > (internal)
> > + * @sg_was_mapped: Set if the scatterlist has been mapped before
> > the request
> > =C2=A0 * @complete: Function called when request completes, so this
> > request and
> > =C2=A0 *	its buffer may be re-used.=C2=A0 The function will always be
> > called with
> > =C2=A0 *	interrupts disabled, and it must not sleep.
> > @@ -111,6 +112,7 @@ struct usb_request {
> > =C2=A0	unsigned		zero:1;
> > =C2=A0	unsigned		short_not_ok:1;
> > =C2=A0	unsigned		dma_mapped:1;
> > +	unsigned		sg_was_mapped:1;
>=20
> why not use dma_mapped direclty?

Because of the unmap case. We want to know whether we should unmap or
not.

>=20
> Frank

Cheers,
-Paul

>=20
> > =C2=A0
> > =C2=A0	void			(*complete)(struct usb_ep *ep,
> > =C2=A0					struct usb_request *req);
> > --=20
> > 2.43.0
> >=20