linux-kernel - Re: [PATCH 4/4] spi: bcm-mspi: Add support to set serial baud clock rate

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Date:	Mon, 6 Apr 2015 11:54:10 -0700
From:	Jonathan Richardson <jonathar@...adcom.com>
To:	Mark Brown <broonie@...nel.org>
CC:	Florian Fainelli <f.fainelli@...il.com>,
	Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazau <anatol@...gle.com>,
	Scott Branden <sbranden@...adcom.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>,
	<linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	<devicetree@...r.kernel.org>, Rafal Milecki <zajec5@...il.com>,
	Brian Norris <computersforpeace@...il.com>,
	Kevin Cernekee <cernekee@...il.com>
Subject: Re: [PATCH 4/4] spi: bcm-mspi: Add support to set serial baud clock
 rate

On 15-04-06 02:46 AM, Mark Brown wrote:
> On Sat, Apr 04, 2015 at 12:12:59PM -0700, Florian Fainelli wrote:
>> Le 02/04/2015 12:23, Jonathan Richardson a écrit :
> 
>>> +		/* Calculate SPBR if clock-frequency provided. */
>>> +		if (of_property_read_u32(dev->of_node, "clock-frequency",
>>> +			&desired_rate) >= 0) {
>>> +			u32 spbr = clk_get_rate(data->clk) / (2 * desired_rate);
> 
>> Usually, specifying a "clock-frequency" property is done when there is
>> no clock provider available, yet we take this code path only if we could
>> find a "mspi_clk" which sounds a litle weird.
> 
>> Once there is a proper "mspi_clk" clock, I would make it mandatory for
>> the clock provider to be able to provide the rate as well?
> 
> As far as I can tell it's already mandatory if the property is present -
> it's taking the clock presented to the block and then using an internal
> divider to bring that down to the desired rate.
> 
> We are missing error handling though.
> 

Thanks for the review. Yes that's correct. I also tried to make it
backwards compatible with the current version of the driver where you
can ignore configuring the frequency. The result being ref clock
frequency / 2 * 255. If you provide the clock then it will
enable/prepare it. If you also provide clock-frequency then it will
configure the SPBR. If you don't provide anything then it works as
before - it assumes the clock is already enabled and uses the h/w
default SPBR.

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