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

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Message-ID: <20200512191910.GD136540@google.com>
Date:   Tue, 12 May 2020 12:19:10 -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>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.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 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?

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