linux-kernel - Re: [PATCH v11]: clk: Add common clock support for Mediatek MT8135 and MT8173

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Message-ID: <CABuKBe+MnmL47FB2FhN=RRKEZV4tR3OyVTTpWfkTYQ4zSZP22Q@mail.gmail.com>
Date:	Wed, 15 Apr 2015 17:11:27 +0200
From:	Matthias Brugger <matthias.bgg@...il.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	YH Chen <yh.chen@...iatek.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Henry Chen <henryc.chen@...iatek.com>,
	linux-mediatek@...ts.infradead.org,
	"=Sascha Hauer" <kernel@...gutronix.de>,
	Yingjoe Chen <Yingjoe.Chen@...iatek.com>,
	Eddie Huang <eddie.huang@...iatek.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v11]: clk: Add common clock support for Mediatek MT8135
 and MT8173

2015-04-14 13:57 GMT+02:00 Sascha Hauer <s.hauer@...gutronix.de>:
> On Tue, Apr 14, 2015 at 01:01:30PM +0200, Matthias Brugger wrote:
>> Hi Sascha,
>>
>> 2015-04-14 12:08 GMT+02:00 Sascha Hauer <s.hauer@...gutronix.de>:
>> > Hi Matthias,
>> >
>> > On Tue, Apr 07, 2015 at 01:47:58PM +0200, Matthias Brugger wrote:
>> >> Hi Sascha,
>> >>
>> >>
>> >> 2015-03-31 20:16 GMT+02:00 Sascha Hauer <s.hauer@...gutronix.de>:
>> >> >
>> >> > The following changes since commit 9eccca0843205f87c00404b663188b88eb248051:
>> >> >
>> >> >   Linux 4.0-rc3 (2015-03-08 16:09:09 -0700)
>> >> >
>> >> > are available in the git repository at:
>> >> >
>> >> >   git://git.pengutronix.de/git/imx/linux-2.6.git tags/v4.0-clk-mediatek-v11
>> >> >
>> >> > for you to fetch changes up to ae9129219143cfdefe8b3a463deb8c5cb8955525:
>> >> >
>> >> >   dt-bindings: ARM: Mediatek: Document devicetree bindings for clock/reset controllers (2015-03-31 20:08:46 +0200)
>> >> >
>> >> > ----------------------------------------------------------------
>> >> > This patchset contains the initial common clock support for Mediatek SoCs.
>> >> > Mediatek SoC's clock architecture comprises of various PLLs, dividers, muxes
>> >> > and clock gates.
>> >>
>> >> I tried the patch set on my mt8135 eval board. I used the dts bindings
>> >> from a former version of this set [1], but it does not boot the board
>> >> (based on v4.0-rc7).
>> >> Do you have any hint, what is happening, or are the bindings wrong?
>> >
>> > I just tried on a v4.0 with
>> > - this series applied
>> > - the dts patch applied (which is still up-to-date)
>> > - multi_v7_defconfig
>> >
>> > And it still works. What do you mean with "does not boot the board"? No
>> > console output? Could you try with earlyprintk?
>>
>> The probelms I see is, that with the clock patches, I'm not able to
>> boot into a initramfs [1].
>> Whereas if I just comment topckgen and preicfg in the dts, I'm able to
>> get the a serial console of my initramfs [2].
>>
>> I wonder if you are able to get serial console from the initramfs with
>> the clock patches + dts patch?
>
> So you get kernel messages but no output from initramfs? In this case
> the kernel disables the unused clocks in a late_initcall. The UART
> driver still uses the dummy clock provided in the dtsi, so the real
> UART clk gets disabled in the initcall. Try passing clk_ignore_unused to
> the kernel

OK, I can boot to the initramfs with this kernel parameter, but it
fails to boot, when I change the uart clock. I suppose that PERI_UART3
for debug port uart3 should be fine, but it looks like it doesn't
work.
I can see on the mt6589 datasheet that you have a register
PERI_UART_CK_SOURCE_SEL where you can decide if you want a 26 MHz or a
52 MHz clock for the UART block.
Does this register exists on mt8135? If so, why is it not implemented?

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