Re: [PATCH v4 7/7] usb: typec: mux: Add On Semi fsa4480 driver

Bjorn Andersson
2022-03-07T14:46:46Z

On Mon 07 Mar 02:16 PST 2022, Andy Shevchenko wrote:

> On Sun, Mar 06, 2022 at 07:40:40PM -0800, Bjorn Andersson wrote:
> > The ON Semiconductor FSA4480 is a USB Type-C port multimedia switch with
> > support for analog audio headsets. It allows sharing a common USB Type-C
> > port to pass USB2.0 signal, analog audio, sideband use wires and analog
> > microphone signal.
> >
> > Due to lacking upstream audio support for testing, the audio muxing is
> > left untouched, but implementation of muxing the SBU lines is provided
> > as a pair of Type-C mux and switch devices. This provides the necessary
> > support for enabling the DisplayPort altmode on devices with this
> > circuit.
>
> ...
>
> > +static const struct regmap_config fsa4480_regmap_config = {
> > + .reg_bits = 8,
> > + .val_bits = 8,
> > + .max_register = FSA4480_MAX_REGISTER,
> > +};
>
> You are using mutex for accessing hardware. Do you still need a regmap lock?
> If so, add a comment to explain why.
>

I've not considered that before, but you're right, there doesn't seem to
be any reason to keep the locking in the regmap.

> ...
>
> > + /* 15us to allow the SBU switch to turn off */
> > + usleep_range(15, 1000);
>
> This is quite unusual range.
>
> If you are fine with the long delay, why to stress the system on it?
> Otherwise the use of 1000 is unclear.
>
> That said, I would expect one of the below:
>
> usleep_range(15, 30);
> usleep_range(500, 1000);
>

Glad you asked about that, as you say the typical form is to keep the
range within 2x of the lower value, or perhaps lower + 5.

But if the purpose is to specify a minimum time and then give a max to
give the system some flexibility in it's decision of when to wake up.
And in situations such as this, we're talking about someone connecting a
cable, so we're in "no rush" and I picked the completely arbitrary 1ms
as the max.

Do you see any drawback of this much higher number? (Other than it
looking "wrong")

> ...
>
> > + sw_desc.fwnode = dev->fwnode;
>
> Please, don't dereference for fwnode explicitly. Use dev_fwnode().
>

Okay, will update accordingly.

Thanks,
Bjorn

> ...
>
> > + mux_desc.fwnode = dev->fwnode;
>
> Ditto.
>
> --
> With Best Regards,
> Andy Shevchenko
>
>