Re: [PATCH] usb: gadget: cdns3: Fix cdns3_ep_config() by setting ep.maxpacket

[Siddharth Vadapalli <s-vadapalli@ti.com>]

On Mon, Oct 07, 2024 at 03:02:34PM +0300, Roger Quadros wrote:

Hello Roger,

> On 07/10/2024 13:42, Siddharth Vadapalli wrote:
> > The function cdns3_ep_config() calculates the maximum packet size based
> > on the Endpoint Type and the Gadget Speed and stores it in the variable
> > "max_packet_size". This value is then programmed in the USB Controller
> > for the corresponding Endpoint. This may result in a mismatch between
> > the maximum packet size programmed in the USB controller and the maximum
> > packet size seen by the UDC Core via "maxpacket" member of "struct usb_ep".
> > Additionally, since TD_SIZE is calculated in cdns3_ep_run_transfer() on the
> > basis of the maximum packet size stored in the "maxpacket" member of
> > "struct usb_ep", it may lead to an incorrect value of TD_SIZE when compared
> > with what the USB controller actually expects (max_packet_size).
> > 

[...]

> > diff --git a/drivers/usb/cdns3/gadget.c b/drivers/usb/cdns3/gadget.c
> > index ac7e469469..b0b08768d9 100644
> > --- a/drivers/usb/cdns3/gadget.c
> > +++ b/drivers/usb/cdns3/gadget.c
> > @@ -1637,6 +1637,14 @@ void cdns3_ep_config(struct cdns3_endpoint *priv_ep)
> >  	else
> >  		priv_ep->trb_burst_size = 16;
> >  
> > +	/*
> > +	 * The Endpoint is configured to handle a maximum packet size of
> > +	 * max_packet_size. Hence, set priv_ep->endpoint.maxpacket to
> > +	 * max_packet_size. This is necessary to ensure that the TD_SIZE
> > +	 * is calculated correctly in cdns3_ep_run_transfer().
> > +	 */
> > +	usb_ep_set_maxpacket_limit(&priv_ep->endpoint, max_packet_size);
> > +
> 
> from include/linux/usb/gadget.h
> 
>  * struct usb_ep - device side representation of USB endpoint
> ...
>  * @maxpacket:The maximum packet size used on this endpoint.  The initial
>  *      value can sometimes be reduced (hardware allowing), according to
>  *      the endpoint descriptor used to configure the endpoint.
>  * @maxpacket_limit:The maximum packet size value which can be handled by this
>  *      endpoint. It's set once by UDC driver when endpoint is initialized, and
>  *      should not be changed. Should not be confused with maxpacket.
> 
> What you want to change is ep->maxpacket and not ep->maxpacket_limit as that is
> fixed for a particular UDC.
> 
> how about?
> 	priv-ep->endpoint.maxpacket = max_packet_size;

Yes, this is accurate. I will post the v2 patch with this change. Thank
you for reviewing the patch.

Regards,
Siddharth.