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

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Date:	Thu, 16 Apr 2015 15:36:35 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Matthias Brugger <matthias.bgg@...il.com>
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

On Wed, Apr 15, 2015 at 05:48:08PM +0200, Matthias Brugger wrote:
> 2015-04-15 17:11 GMT+02:00 Matthias Brugger <matthias.bgg@...il.com>:
> > 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?
> 
> I found that PERI_UARTx_CK is connected to axi_sel but should be
> connected to uart_sel. Like this I'm able to reach to initramfs
> console, but the baud rate values are screwed up.
> As uart_sel is at 52 MHz, I suppose we need to change the entries in
> PERI_UART_CK_SOURCE_SEL.

I just asked the Mediatek guys for clarification, lets see what they
tell me. There is a PERI_UART_CK_SOURCE_SEL on MT8135/MT8173, I have no
idea why this is not implemented. I also don't know where the clocks I
can select in the PERI_UART_CK_SOURCE_SEL register are derived from.
It's also unclear to me how the real UART clock topology looks like.

Sascha

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