linux-kernel - Re: [PATCH V4 1/5] phy: Add new Exynos5 USB 3.0 PHY driver

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Date:	Tue, 22 Apr 2014 11:18:41 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Vivek Gautam' <gautam.vivek@...sung.com>,
	'Tomasz Figa' <t.figa@...sung.com>
Cc:	'Linux USB Mailing List' <linux-usb@...r.kernel.org>,
	linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	'kishon' <kishon@...com>, 'Greg KH' <gregkh@...uxfoundation.org>,
	'Felipe Balbi' <balbi@...com>,
	'Kukjin Kim' <kgene.kim@...sung.com>,
	'Kamil Debski' <k.debski@...sung.com>,
	'Sylwester Nawrocki' <sylvester.nawrocki@...il.com>,
	'Jingoo Han' <jg1.han@...sung.com>
Subject: Re: [PATCH V4 1/5] phy: Add new Exynos5 USB 3.0 PHY driver

On Wednesday, April 16, 2014 11:49 PM, Vivek Gautam wrote:
> On Wed, Apr 16, 2014 at 7:14 PM, Tomasz Figa <t.figa@...sung.com> wrote:
> > On 15.04.2014 08:09, Vivek Gautam wrote:
> >> On Thu, Apr 10, 2014 at 5:09 PM, Vivek Gautam wrote:
> >>> On Wed, Apr 9, 2014 at 7:03 PM, Tomasz Figa <t.figa@...sung.com> wrote:
> >>>> On 09.04.2014 13:49, Vivek Gautam wrote:
> >>>
> >>> So, USB30_SCLK_100M is the SCLK that we are talking in the driver. I
> >>> don't see any reference to XXTI in the USB 3.0 DRD controller chapter
> >>> (in both Exynos5250 and 5420)
> >>> In addition to this there's one more point to be noticed here.
> >>> On Exynos5420 system, the sclk_usbphy300 (which is the sclk_usbphy30
> >>> for USB DRD channel 0), is also the PICO phy clock, i.e. USB 2.0 phy
> >>> clock.
> >>> So we should add a similar clk_get() for this clock in the
> >>> phy-exynos5250-usb2 driver too, to support Exynos5420.
> >>
> >>
> >> Is something clear from the above block diagram ? (although the
> >> diagram looks weird - space and tabs problem :-(  )
> >> Basically there's the clock USB30_SCLK_100M which is going into the
> >> USB 3.0 DRD PHY controller.
> >> And this is the only sclk mentioned in the block diagram for USB 3.0
> >> DRD controller in Exynos5420.
> >> Same is not there in the block diagram in Exynos5250 UM.
> >
> >
> > From what I can see in the documentation, there are 4 USB 3.0 related clocks
> > generated in CMU:
> >
> >  - sclk_usbphy300,
> >  - sclk_usbphy301,
> >  - sclk_usbdrd300,
> >  - sclk_usbdrd301,
> >
> > They are all rated to max. 24 MHz and the recommended operating frequency is
> > 24 MHz, so it looks exactly like USB PHY reference, which is usually a 24
> > MHz clock.
> >
> > To me, this looks like on Exynos5420 a separate special clock path is used
> > instead of xusbxti as reference of USB 3.0 PHY and so the sclk should be
> > simply passed as the "ref" clock.
> 
> Ok, i will clear on this with the hardware engineer also once.
> May be Jingoo can help me with this.
> 
> Jingoo,
> Can you please enquire about the clock path of usbphy30 reference
> clocks on Exynos5420.
> As mentioned by Tomasz above, we have sclk_usbphy300 and
> sclk_usbphy301 as the reference clocks for USB3.0 DRD phy. *Also*
> sclk_usbphy300 is used for Pico phy (which is the USb 2.0 phy used by
> ehci/ohci controller on Exynos5420).
> It will be of great help.

Hi Vevek, Tomasz

Long time no see.

I asked USB S/W engineer and USB H/W engineer.

There are two USB3.0 on Exynos5420; thus there are two sclks
such as 'sclk_usbphy300 and sclk_usbphy301'.

As Tomasz mentioned, 'sclk_usbphy300 and sclk_usbphy301' can
be used instead of 'xusbxti' as reference of USB 3.0 PHY.

However, on Exynos5420, "ONLY" 'sclk_usbphy300' can be used
for USB2.0 pico phy. (so, '301' CANNOT support USB2.0 pico phy.)

Best regards,
Jingoo Han

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