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

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Message-ID: <20150406094636.GC6023@sirena.org.uk>
Date:	Mon, 6 Apr 2015 10:46:36 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Jonathan Richardson <jonathar@...adcom.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 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.

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