linux-kernel - Re: [PATCH 2/4] usb: typec: mux: intel_pmc_mux: Support for static SBU/HSL orientation

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Message-ID: <CACeCKad4BebiBJS_wO=FdWVWypgOD822Dir7HeRBf0uXUuJusA@mail.gmail.com>
Date:   Thu, 14 May 2020 13:51:32 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benson Leung <bleung@...omium.org>,
        "open list:USB NETWORKING DRIVERS" <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-acpi@...r.kernel.org,
        Tim Wawrzynczak <twawrzynczak@...omium.org>
Subject: Re: [PATCH 2/4] usb: typec: mux: intel_pmc_mux: Support for static
 SBU/HSL orientation

Hi Heikki,

On Tue, May 12, 2020 at 12:19 PM Prashant Malani <pmalani@...omium.org> wrote:
>
> Hi Heikki,
>
> On Tue, May 12, 2020 at 05:22:51PM +0300, Heikki Krogerus wrote:
> > Hi Prashant,
> >
> > On Mon, May 11, 2020 at 10:57:19AM -0700, Prashant Malani wrote:
> > > Hi Heikki,
> > >
> > > Thanks a lot for looking into this. Kindly see my response inline:
> > >
> > > On Mon, May 11, 2020 at 04:32:02PM +0300, Heikki Krogerus wrote:
> > > > On Fri, May 08, 2020 at 02:18:44PM +0300, Heikki Krogerus wrote:
> > > > > Hi Prashant,
> > > > >
> > > > > On Thu, May 07, 2020 at 03:40:41PM -0700, Prashant Malani wrote:
> > > > > > > +static int sbu_orientation(struct pmc_usb_port *port)
> > > > > > > +{
> > > > > > > +   if (port->sbu_orientation)
> > > > > > > +           return port->sbu_orientation - 1;
> > > > > > > +
> > > > > > > +   return port->orientation - 1;
> > > > > > > +}
> > > > > > > +
> > > > > > > +static int hsl_orientation(struct pmc_usb_port *port)
> > > > > > > +{
> > > > > > > +   if (port->hsl_orientation)
> > > > > > > +           return port->hsl_orientation - 1;
> > > > > > > +
> > > > > > > +   return port->orientation - 1;
> > > > > > > +}
> > > > > > > +
> > > > > > >  static int pmc_usb_command(struct pmc_usb_port *port, u8 *msg, u32 len)
> > > > > > >  {
> > > > > > >     u8 response[4];
> > > > > > > @@ -151,8 +170,9 @@ pmc_usb_mux_dp(struct pmc_usb_port *port, struct typec_mux_state *state)
> > > > > > >
> > > > > > >     req.mode_data = (port->orientation - 1) << PMC_USB_ALTMODE_ORI_SHIFT;
> > > > > > >     req.mode_data |= (port->role - 1) << PMC_USB_ALTMODE_UFP_SHIFT;
> > > > > > > -   req.mode_data |= (port->orientation - 1) << PMC_USB_ALTMODE_ORI_AUX_SHIFT;
> > > > > > > -   req.mode_data |= (port->orientation - 1) << PMC_USB_ALTMODE_ORI_HSL_SHIFT;
> > > > > > > +
> > > > > > > +   req.mode_data |= sbu_orientation(port) << PMC_USB_ALTMODE_ORI_AUX_SHIFT;
> > > > > >
> > > > > > I'm curious to know what would happen when sbu-orientation == "normal".
> > > > > > That means |port->sbu_orientation| == 1.
> > > > > >
> > > > > > It sounds like what should happen is the AUX_SHIFT orientation
> > > > > > setting should follow what |port->orientation| is, but here it
> > > > > > looks like it will always be set to |port->sbu_orientation - 1|, i.e 0,
> > > > > > even if port->orientation == TYPEC_ORIENTATION_REVERSE, i.e 2, meaning
> > > > > > it should be set to 1 ?
> > > > >
> > > > > I'll double check this, and get back to you..
> > > >
> > > > This is not exactly an answer to your question, but it seems that
> > > > those bits are only valid if "Alternate-Direct" message is used.
> > > > Currently the driver does not support that message.
> > > Could you kindly provide some detail on when "Alternate-Direct" would be
> > > preferred to the current method?
> >
> > Alternate Mode Direct request is supposed to be used if an alternate
> > mode is entered directly from disconnected state.
>
> Ack.
> >
> > > Also, is there anything on the PMC side which is preventing the use of
> > > "Alternate-Direct" messages? It seems like the state transition diagram
> > > there would be simpler, although I'm likely missing significant details
> > > here.
> >
> > So we actually should use the "direct" request if we are in
> > disconnected state to enter alt modes if I understood correctly. But
> > otherwise we should use the normal Alternate Mode request and not the
> > Alternate Mode "direct" request. And I'm afraid I don't know why.
>
> SG.
> >
> > > > I think the correct thing to do now is to remove the two lines from
> > > > the driver where those bits (ORI-HSL and ORI-Aux) are set.
> > > I see. How would orientation then be handled in a retimer configuration
> > > where AUX/SBU is flipped by the retimer itself?
> >
> > Note that if we send a separate "connection" request first, then we
> > already tell the HSL and SBU orientation as part of the payload of
> > that request. That is why there is no need to tell about the HSL and
> > SBU orientation with the normal Alternate Mode Request.
> >
> > So we have already handled the HSL and SBU orientation by the time
> > this function is called.
>
> Thanks for the explanation. I assume the HSL and SBU bit setting lines
> will be removed from pmc_usb_mux_tbt() too?
>
I just realized, the issue I initially pointed out would apply to the
connect message too, i.e I'm not sure if "normal" orientation setting
handles the case where port orientation is reversed correctly.
Overall, I am not sure that re-using the typec_orientations[] string
list is the best option for this use-case.
we're looking for "normal" (i.e follows port->orientation) and "fixed"
(i.e is always the same orientation, regardless of what
port->orientation is), so it is perhaps better to just define a new
array just for this driver.

> Best regards,
> >
> >
> > thanks,
> >
> > --
> > heikki