linux-kernel - Re: [PATCH 0/7] ARM: berlin: refactor the clock

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Date:	Mon, 16 Feb 2015 11:46:58 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Antoine Tenart <antoine.tenart@...e-electrons.com>
CC:	"sebastian.hesselbarth@...il.com" <sebastian.hesselbarth@...il.com>,
	"mturquette@...aro.org" <mturquette@...aro.org>,
	"sboyd@...eaurora.org" <sboyd@...eaurora.org>,
	Jimmy Xu <zmxu@...vell.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] ARM: berlin: refactor the clock

Hi all,

On Sun, 15 Feb 2015 19:37:38 -0800
Jisheng Zhang <jszhang@...vell.com> wrote:

> Hi all,
> 
> On Fri, 13 Feb 2015 08:42:54 -0800
> Antoine Tenart <antoine.tenart@...e-electrons.com> wrote:
> 
> > Hi,
> > 
> > Marvell Berlin SoCs have a chip control register set providing several
> > individual registers dealing with various controllers (pinctrl, reset,
> > clk). This chip controller is described by a single DT node since the
> > individual registers are spread among the chip control register bank.
> > 
> > Marvell Berlin also have a system control register set providing several
> > individual registers for pinctrl or adc.
> 
> There's no chip control IP. The HW just put some HW registers into the so
> called "chip control" address space, the registers in this space are mostly
> used for "control" purpose, but some are not. Take the clk as an example,
> some clocks' registers are put into the system control register space, some
> clocks' are not.
> 
> So far, there are five type of clocks in Berlin (from the driver
> programmer's point of view):
> 
> 1. gate clocks. The clocks may share register. The clocks can only be gated
> or ungated.
> 
> 2. individual clocks. The clock doesn't share registers with each other.
> The gate/ungate, clock source selection, clock divider etc. bits of each
> clock are put into one individual register. one register per clock.
> 
> 3. group clocks. The gate/ungate bits of these clocks are grouped into one
> register, the clock source selection, clock divider bits of these clocks
> are grouped into another one or two register.
> 
> 4. plls. The pll doesn't share registers with each other. For example,
> syspll, cpupll etc. one or two register per pll
> 
> 5. fixed clock. the oscillator used for reference clock.
> 
> In newer chips, there are no group clocks any more. So the driver code can
> be more simpler and clean.
> 
> So I think we'd better to implement drivers without the "chip control"
> concept in mind. The previous clock patches reflect what the HW really does.
> 
> https://lkml.org/lkml/2014/3/21/413
> 
> https://lkml.org/lkml/2014/4/24/624

To be honest, these two patches are what mrvl used internally. And for newer
linux kernel version, we replaced the mainline clk driver with this mrvl specific
one.

> 
> 
> The above is just my humble opinions and the current berlin clk driver is
> different with the previous one I dunno how can we handle this situation
> now. I really need help!
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