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

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Date:	Thu, 20 Aug 2015 12:05:20 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Tony Lindgren <tony@...mide.com>, <balbi@...com>
CC:	<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

Hi,

On Thursday 06 August 2015 02:17 PM, Tony Lindgren wrote:
> * 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.

OMAP4 uses UTMI PHY and it uses CONTROL_USBOTGHS_CONTROL too.
> 
> 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.

hmm.. IMHO CONTROL_USBOTGHS_CONTROL register belongs to the TI MUSB glue and
should be programmed in omap2430.c. It's better to get the opinion of Felipe
here. Felipe?
> 
> 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?

Not in phy-omap-usb2.c. It's the UTMI PHY driver and is not used by OMAP3 based
boards (uses twl4030 ULPI PHY). CONTROL_USBOTGHS_CONTROL has to be programmed
for OMAP3 also.

Thanks
Kishon
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