Re: [PATCH] usb: dwc3: core: Do core softreset when switch mode

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Apr 15, 2021 at 07:10:34AM +0000, Thinh Nguyen wrote:
> Felipe Balbi wrote:
> > 
> > Hi,
> > 
> > Thinh Nguyen <Thinh.Nguyen@synopsys.com> writes:
> >> From: Yu Chen <chenyu56@huawei.com>
> >> From: John Stultz <john.stultz@linaro.org>
> >>
> >> According to the programming guide, to switch mode for DRD controller,
> >> the driver needs to do the following.
> >>
> >> To switch from device to host:
> >> 1. Reset controller with GCTL.CoreSoftReset
> >> 2. Set GCTL.PrtCapDir(host mode)
> >> 3. Reset the host with USBCMD.HCRESET
> >> 4. Then follow up with the initializing host registers sequence
> >>
> >> To switch from host to device:
> >> 1. Reset controller with GCTL.CoreSoftReset
> >> 2. Set GCTL.PrtCapDir(device mode)
> >> 3. Reset the device with DCTL.CSftRst
> >> 4. Then follow up with the initializing registers sequence
> >>
> >> Currently we're missing step 1) to do GCTL.CoreSoftReset and step 3) of
> > 
> > we're not really missing, it was a deliberate choice :-) The only reason
> > why we need the soft reset is because host and gadget registers map to
> > the same physical space within dwc3 core. If we cache and restore the
> > affected registers, we're good ;-)
> 
> It's part of the programming model. I've already discussed with internal
> RTL designers. This is needed, and I've provided the discussion we had
> prior also. We have several different devices in the wild that need
> this. What is the concern?
> 
> > 
> > IMHO, that's a better compromise than doing a full soft reset.
> > 
> >> @@ -40,6 +41,8 @@
> >>  
> >>  #define DWC3_DEFAULT_AUTOSUSPEND_DELAY	5000 /* ms */
> >>  
> >> +static DEFINE_MUTEX(mode_switch_lock);
> > 
> > there are several platforms which more than one DWC3 instance. Sure this
> > won't break on such systems?
> > 
> 
> How? Am I missing something? Please let me know so I can make the change.

All data needs to be per-device, not "global for the codebase" like the
way you declared this lock.

thanks,

greg k-h