linux-kernel - Re: [PATCH v3 2/7] clk: rockchip: rk3399: export 480M

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Message-ID: <f9312de8-7f7c-b6e1-0eec-ac78813cc2b0@rock-chips.com>
Date:	Mon, 8 Aug 2016 17:55:10 +0800
From:	Frank Wang <frank.wang@...k-chips.com>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	Xing Zheng <zhengxing@...k-chips.com>,
	linux-rockchip@...ts.infradead.org, dianders@...omium.org,
	briannorris@...omium.org, huangtao@...k-chips.com,
	zhangqing@...k-chips.com, wulf@...k-chips.com,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>, linux-clk@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	daniel.meng@...k-chips.com, frank.wang@...k-chips.com
Subject: Re: [PATCH v3 2/7] clk: rockchip: rk3399: export 480M_SRC clock id
 for usbphy0/usbphy1

Hi Heiko,

On 2016/8/6 0:05, Heiko Stübner wrote:
> Hi Frank,
>
> Am Freitag, 5. August 2016, 16:34:42 schrieb Frank Wang:
>> On 2016/8/5 3:10, Heiko Stübner wrote:
>>> Am Dienstag, 2. August 2016, 15:19:56 schrieb Xing Zheng:
>>>> Export these source clocks for usbphy.
>>>>
>>>> Signed-off-by: Xing Zheng <zhengxing@...k-chips.com>
>>> can you please provide a rationale why you need manual control over that
>>> intermediate clock?
>> Well, From below graph, you can see that 'clk_usbphyX_480m' is generated
>> from usb2phy, and 'clk_usbphy_480m' which select from
>> clk_usbphyX_480m_src via a gate (G13[12])  provided 480M clock to other
>> modules.
>>
>>     xin24m
>>       |__ clk_usb2phy0_ref
>>       |     |
>>       |     |__ clk_usbphy0_480m
>>       |           |
>>       |           |__clk_usbphy0_480m_src
>>       |                |
>>       |                |__clk_usbphy_480m
>>       |                     |__ ... ...
>>       |
>>       |__ clk_usb2phy1_ref
>>             |
>>             |__ clk_usbphy1_480m
>>                   |
>>                   |__clk_usbphy1_480m_src
>>> The two usbphys seem to use the  clk_usb2phyX_ref clocks, generate the
>>> 480m
>>> clocks, but do not seem to need the clk_usbphyX_480m_src gates.
>> Yeah, they used to be. However, the story went something like this,
>>
>> Some PM suspend process related ehci/ohci controller are base on 480m
>> clocks, unfortunately, usb2-phy suspended earlier than ehci/ohci
>> (usb2-phy will be auto suspended if no devices plug-in), and the
>> clk-480m provided by it was disabled if no module used. As a result, the
>> PM suspend process was blocked when it run into ehci/ohci module.
> ah, so the ehci controller needs that 480m clock as well? Do you happen to
> have example patches for the ehci/ohci side already? I'd like to peak at what
> you mean with "some PM suspend process related" things.

Actually, no patches for it, I just make below steps manually :-).
1. set two usb2-phy into suspend mode.
2. disable 480m clock on each usb2-phy (assume only usb2-phy used it).
3. press power button let system into PM suspend.

Then, the kernel will be blocked and you can see the following log from 
console.
... ....
[  123.763848] calling  usb6+ @ 166, parent: xhci-hcd.0.auto
[  123.764503] call usb6+ returned 0 after 163 usecs
[  123.765106] calling  usb5+ @ 166, parent: xhci-hcd.0.auto
[  123.765719] call usb5+ returned 0 after 121 usecs
[  123.766294] calling  usb4+ @ 166, parent: fe3e0000.usb
[  123.766917] calling  usb3+ @ 55, parent: fe3a0000.usb

>
> Depending on what is actually needed, you could also pull the usbphy out of
> autosuspend in a pm-prepare callback of the phy driver itself ... see
> http://lxr.free-electrons.com/source/include/linux/pm.h#L86
>
> Like
> - in the .prepare callback make sure to unsuspend the phy
>    and deactivate the autosuspend
> - ehci/ohci will poweroff the phy in it s suspend callback (already does that)

Hmm, do you remember that we have previously discussed there are some 
oddities in ehci/ohci driver? phy_power_on() gets called twice at 
ehci/ohci driver probe time, one is at pdata->power_on(); another is at 
usb_add_hcd(), then the power_count of phy increases to 2,  but 
phy_power_off() is just invoked one time when ehci/ohci goes to PM 
suspend, so phy->ops->power_off is never be invoked.

In this way,  the usb-phy maybe never go to suspend.

> - suspend -> resume
> - ehci/ohci will poweron the phy
> - in the phy's .complete callback you can reactivate the autosuspend timer
>
> Because it looks more like you actually need the phy and not the clock alone.
> So it would be nicer to use mechanisms already in place instead of creating
> new dependencies.
>

Theoretically, phy_init() will be invoked when ehci/ohci power on, and 
the sm_work will be reactivated (have already implemented) in 
phy->ops->init, but unfortunately, the same issue as phy_power_on() 
mentioned above, it never run there too .

>> Hence, we are planing to refer clk_usbphyX_480m_src into each ehci/ohci
>> driver. Maybe you will challenge why not refer clk_usbphy_480m directly?
>> because there are two ehci/ohci connected in the different usb2phy, and
>> only one clk_usbphy_480m clock was selected in clock tree.
> Nope, no argument from me as I fully understand that each phy provides its own
> 480m clock :-) .
>
>
> Heiko
>
>