Message-ID: <5522D652.4020205@broadcom.com>
Date: Mon, 6 Apr 2015 11:54:10 -0700
From: Jonathan Richardson <jonathar@broadcom.com>
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To: Mark Brown <broonie@kernel.org>
CC: Florian Fainelli <f.fainelli@gmail.com>, Dmitry Torokhov <dtor@google.com>,
        Anatol Pomazau <anatol@google.com>,
        Scott Branden <sbranden@broadcom.com>,
        Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, <linux-kernel@vger.kernel.org>,
        <linux-spi@vger.kernel.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@broadcom.com>,
        <devicetree@vger.kernel.org>, Rafal Milecki <zajec5@gmail.com>,
        Brian Norris <computersforpeace@gmail.com>,
        Kevin Cernekee <cernekee@gmail.com>
Subject: Re: [PATCH 4/4] spi: bcm-mspi: Add support to set serial baud clock
 rate
References: <1428002603-21892-1-git-send-email-jonathar@broadcom.com> <1428002603-21892-5-git-send-email-jonathar@broadcom.com> <552037BB.7050803@gmail.com> <20150406094636.GC6023@sirena.org.uk>
In-Reply-To: <20150406094636.GC6023@sirena.org.uk>
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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 ?crit :
> 
>>> +		/* 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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