linux-kernel - Re: [PATCH v4 22/22] phy: Add support for Qualcomm's USB HS phy

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Date:   Wed, 14 Sep 2016 10:11:33 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Stephen Boyd <stephen.boyd@...aro.org>
Cc:     linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Andy Gross <andy.gross@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Arnd Bergmann <arnd@...db.de>, Felipe Balbi <balbi@...nel.org>,
        Peter Chen <peter.chen@....com>,
        Kishon Vijay Abraham I <kishon@...com>,
        devicetree@...r.kernel.org,
        Fabien Lahoudere <fabien.lahoudere@...labora.co.uk>
Subject: Re: [PATCH v4 22/22] phy: Add support for Qualcomm's USB HS phy

On Tue, Sep 13, 2016 at 01:41:44PM -0700, Stephen Boyd wrote:
> Quoting Peter Chen (2016-09-13 00:03:58)
> > On Wed, Sep 07, 2016 at 02:35:19PM -0700, Stephen Boyd wrote:
> > > The high-speed phy on qcom SoCs is controlled via the ULPI
> > > viewport.
> > > 
> > 
> > Hi Stephen, I am a little puzzled how this driver co-work with chipidea
> > driver. According to nxp IC guys, the ULPI PHY's clock needs to be enabled
> > before access portsc.pts (calling hw_phymode_configure), otherwise,
> > the system will hang. But I find you call hw_phymode_configure before
> > phy->power_on, doesn't your design have this requirement?
> 
> Which clk needs to be enabled? The xcvr_clk? I believe that clk
> corresponds to the "core" clk that we enable in the msm glue driver
> layer. When that clk is enabled, the ULPI phy is able to respond to
> register read/writes via the ULPI viewport.
> 

The input clock for ULPI PHY, maybe it is ref_clk at this PHY driver, 
so in your platform, even PHY clock is gated, you can still access
portsc.pts to configure PHY mode at controller register?

> >        
> > Besides, you read ulpi id before phy->power_on, how can read work before
> > phy power on?
> > 
> 
> I've found that even having the link clk enabled before phy->power_on
> doesn't mean it's possible to read the id registers though. That's
> because there can be other power supplies, like regulators, which need
> to be on for the phy to operate properly.
> 

Then I am puzzled the current initialization for your case, in my mind,
it should like below:

qcom_usb_hs_phy_probe->qcom_usb_hs_phy_power_on->ci_ulpi_init

Like other PHYs, it should get PHY first, then power on it, after that,
you can access its register.

-- 

Best Regards,
Peter Chen