linux-kernel - Re: clock driver

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Date:	Tue, 26 May 2015 17:32:13 -0700
From:	York Sun <yorksun@...escale.com>
To:	Guenter Roeck <linux@...ck-us.net>, <mturquette@...aro.org>
CC:	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<lee.jones@...aro.org>, <andrey@...hel.com>,
	<sebastian.hesselbarth@...il.com>, <rabeeh@...id-run.com>
Subject: Re: clock driver

Michael,

Can you give me some guidance here?


On 05/26/2015 05:20 PM, York Sun wrote:
> 
> 
> On 05/26/2015 03:38 PM, Guenter Roeck wrote:
>> On Tue, May 26, 2015 at 12:12:11PM -0700, York Sun wrote:
>>> Linux experts,
>>>
>>> I have rewritten a driver for Silicon Labs SI5338 programmable clock chip. The
>>> original driver was written by Andrey (CC'ed), but was floatingn outside of the
>>> kernel. The driver was written to use sysfs as the interface, not the common
>>> clock framework. I wonder if I have to rewrite the driver following common clock
>>> framework. One concern is to support a feature to accept ClockBuilder (TM)
>>> output on sysfs. I don't see sysfs support on common clock framework. Please
>>> correct me if I am wrong.
>>>
>>> If not using common clock framework is acceptable, I would like to send a RFC
>>> patch for review.
>>>
>> My original driver for si570 was rejected because it didn't support the clock
>> framework, so you might face an uphill battle.
>>
>> SI provides a document for SI5338 describing how to configure it without
>> using clockbuilder [1]. Can that be used to implement generic code which
>> doesn't need clockbuilder ?
>>
> 
> The driver is capable to handle the user's input and enable the clocks. Removing
> the support of importing is a step back. At least it is a feature I am using. I
> believe Andrey also used this feature when the driver was first drafted.
> 
> That being said, my application relies on setting multiple clock chips on a PCIe
> device. That means I cannot put the configuration into device tree. There may be
> a way to fill device tree, but I am not ready to explore yet. Without a sysfs
> interface, can I change the configuration for each clock?
> 
> I also found COMMON_CLK is a bool, not tristate. It is only selected by others.
> Is there a reason for doing so? My current platform (P1022DS) doesn't have
> CONFIG_COMMON_CLK enabled.
> 

If converting my driver to common clock framework, I need to find a way to
configure the clocks without recompiling the kernel. I will have about 30 clock
chips (with different frequency) on multiple PCIe cards.

York
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