linux-kernel - Re: [PATCH] usb: gadget: Support transfers from device memory

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Message-ID: <2023103156-clapping-shed-4626@gregkh>
Date:   Tue, 31 Oct 2023 07:00:43 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Manan Aurora <maurora@...gle.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        manugautam@...gle.com
Subject: Re: [PATCH] usb: gadget: Support transfers from device memory

On Tue, Oct 31, 2023 at 03:54:02AM +0000, Manan Aurora wrote:
> USB gadget stack only supports usb_request objects that point to buffers
> located in memory. Support use cases where data is transferred from
> physical addresses in device mmio regions
> 
> Added a bit "pre_mapped" to usb_request to bypass dma_map_single and
> dma_map_sg for such requests
> 
> The caller must determine the dma address for the request before queuing
> it
> 
> Signed-off-by: Manan Aurora <maurora@...gle.com>
> ---
>  drivers/usb/gadget/udc/core.c | 4 ++--
>  include/linux/usb/gadget.h    | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index ded9531f141b..236165ba08f4 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c
> @@ -900,7 +900,7 @@ EXPORT_SYMBOL_GPL(usb_gadget_activate);
>  int usb_gadget_map_request_by_dev(struct device *dev,
>  		struct usb_request *req, int is_in)
>  {
> -	if (req->length == 0)
> +	if (req->pre_mapped || req->length == 0)
>  		return 0;
>  
>  	if (req->num_sgs) {
> @@ -948,7 +948,7 @@ 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->pre_mapped || req->length == 0)
>  		return;
>  
>  	if (req->num_mapped_sgs) {
> diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
> index a771ccc038ac..6bc035439098 100644
> --- a/include/linux/usb/gadget.h
> +++ b/include/linux/usb/gadget.h
> @@ -111,6 +111,7 @@ struct usb_request {
>  	unsigned		zero:1;
>  	unsigned		short_not_ok:1;
>  	unsigned		dma_mapped:1;
> +	unsigned		pre_mapped:1;
>  
>  	void			(*complete)(struct usb_ep *ep,
>  					struct usb_request *req);
> -- 
> 2.42.0.820.g83a721a137-goog
> 
> 

You can not add features/functionality that no in-kernel driver uses, so
this can not be accepted as-is, sorry.  Please submit it as part of a
patch series where it is actually used, otherwise we have no idea if
this is even something that we should do or not.

thanks,

greg k-h