linux-kernel - Re: [PATCH v2 03/11] ARM: davinci: da850: use clk->set

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Message-ID: <56F2D27F.6040001@ti.com>
Date:	Wed, 23 Mar 2016 22:59:35 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	David Lechner <david@...hnology.com>
CC:	Petr Kulhavy <petr@...ix.com>, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Kevin Hilman <khilman@...nel.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Bin Liu <b-liu@...com>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Andreas Färber <afaerber@...e.de>,
	Tony Lindgren <tony@...mide.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2 03/11] ARM: davinci: da850: use clk->set_parent for
 async3

On Wednesday 23 March 2016 10:50 PM, David Lechner wrote:
> On 03/23/2016 10:56 AM, Sekhar Nori wrote:
>> On Thursday 17 March 2016 07:56 AM, David Lechner wrote:
>>> The da850 family of processors has an async3 clock domain that can be
>>> muxed to either pll0_sysclk2 or pll1_sysclk2. Now that the davinci
>>> clocks
>>> have a set_parent callback, we can use this to control the async3 mux
>>> instead of a stand-alone function.
>>>
>>> This adds a new async3_clk and sets the appropriate child clocks. The
>>> default is use to pll1_sysclk2 since it is not affected by processor
>>> frequency scaling.
>>>
>>> Signed-off-by: David Lechner <david@...hnology.com>
>>> ---
>>
>>> +static int da850_async3_set_parent(struct clk *clk, struct clk *parent)
>>> +{
>>> +    u32 __iomem *cfgchip3;
>>> +    u32 val;
>>> +
>>> +    /*
>>> +     * Can't use DA8XX_SYSCFG0_VIRT() here since this can be called
>>> before
>>> +     * da8xx_syscfg0_base is initialized.
>>> +     */
>>> +    cfgchip3 = ioremap(DA8XX_SYSCFG0_BASE + DA8XX_CFGCHIP3_REG, 4);
>>
>> Is this just a theoretical possibility or have you seen this happen? I
>> would like to see if there are ways of avoiding this rather than throw
>> away usage of DA8XX_SYSCFG0_VIRT()
> 
> Yes, it will not boot without this. The problem comes from the fact that
> clocks are setup in davinci_common_init() which is called before
> da8xx_syscfg0_base = ioremap(DA8XX_SYSCFG0_BASE, SZ_4K) in da850_init()
> (and da830_init()). I also tried moving the ioremap() before
> davinci_common_init(), but davinci_common_init() sets up the iomem, so
> that doesn't work either.
> 
> So, if you want to use DA8XX_SYSCFG0_VIRT() here, the clock init would
> have to be split out from davinci_common_init() which would affect all
> davinci devices.

Alright, I guess 'can be called' in the comment should have used
stronger language :) How about late registration of USB clocks as I
suggested. It should also help consolidate code across da830 and da850.

Thanks,
Sekhar