linux-kernel - Re: [PATCH] usb: musb: omap2430: use *syscon* framework API to write to mailbox register

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Message-ID: <20150806084716.GB4215@atomide.com>
Date:	Thu, 6 Aug 2015 01:47:16 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Kishon Vijay Abraham I <kishon@...com>
Cc:	balbi@...com, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-omap@...r.kernel.org, nsekhar@...com,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH] usb: musb: omap2430: use *syscon* framework API to write
 to mailbox register

* Kishon Vijay Abraham I <kishon@...com> [150805 07:10]:
> On Wednesday 05 August 2015 01:31 PM, Tony Lindgren wrote:
> > 
> > We don't have syscon-otghs and to me it seems we need a PHY driver
> > as I pointed out at:
> 
> If *syscon-otghs* is not present, then it'll fall-back to using the *ctrl-module*.

OK great.

> > 
> > https://lkml.org/lkml/2015/6/24/231
> 
> Maybe I should have explained this in the previous thread. The *otghs* register
> that we are trying to access here does _not_ belong to the PHY. It acts as
> mailbox register from MUSB glue (TI integration layer) to MUSB core. That's why
> it's programmed in the TI glue layer (omap2430.c).
> 
> Even when we were using the older API [omap_control_usb_set_mode()], we first
> call omap_musb_mailbox from the PHY drivers (phy-twl4030-usb.c,
> phy-twl6030-usb.c) and then omap_musb_mailbox in the TI glue writes to the
> control module instead of PHY drivers directly calling omap_control_usb_set_mode().

Hmm looking at "Table 18-204. CONTROL_USBOTGHS_CONTROL" it seems to mention
"transceiver" for quite a few bitfields :) Probably what that register does
is control a PHY over ULPI.

So from Linux kernel point of view we're best off treating it as a PHY.
It seems it should have a minimal PHY driver similar to what we have for
dm816x control module in drivers/phy/phy-dm816x-usb.c.

For reference, here is the register bitfields pasted from 4460 TRM:

Table 18-204. CONTROL_USBOTGHS_CONTROL, p3972
Physical Address 0x4A00 233C

BIT	NAME		DESCIPTION
8	DISCHRGVBUS	... OTG transceiver does (not) discharge VBUS ...
7	CHRGVBUS	... OTG transceiver does (not) charge VBUS ...
6	IDPULLUP	... OTG transceiver does (not) drive VBUS ...
4	IDDIG		... OTG transceiver does (not) apply a pullup to ID ...
3	SESSEND		... VBUS voltage is above/below VB_SESS_END ...	
2	VBUSVALID	... VBUS is above the threshold ...
1	BVALID		... VBUS voltage is above/below VB_SESS_VLD ...
0	AVALID		... BUS voltage is above/below VA_SESS_VLD ...

So how about just adding ONTROL_USBOTGHS_CONTROL support to the existing
drivers/phy/phy-omap-usb2.c instead? It seems that it should allow us
to completely get rid of the custom mailbox stuff for MUSB 2430 support?

> > So let's sort that issue first. It also seems this just completely
> > breaks the MUSB support?
> 
> Why do you think so? If *syscon-otghs* is not present in dt, then it'll
> fall-back to using the *ctrl-module* and everything should work seamlessly.

OK that's good to hear. IMO drivers/phy/phy-omap4.c or similar should
manage the syscon-otghs syscon register, not MUSB driver.

Regards,

Tony
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