linux-kernel - Re: [PATCH v3 6/8] phy: miphy28lp: Add SSC support for PCIE

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Message-ID: <CAG374jBJcX00S4nSugWXaUxAQV3Bwp+OxY0c2GJ-+rskzDzpGw@mail.gmail.com>
Date:	Mon, 13 Oct 2014 10:16:06 +0200
From:	Gabriel Fernandez <gabriel.fernandez@...aro.org>
To:	Valdis.Kletnieks@...edu
Cc:	Gabriel FERNANDEZ <gabriel.fernandez@...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>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>,
	Patrice Chotard <patrice.chotard@...com>,
	Russell King <linux@....linux.org.uk>,
	Kishon Vijay Abraham I <kishon@...com>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kernel@...inux.com" <kernel@...inux.com>,
	Lee Jones <lee.jones@...aro.org>,
	Harsh Gupta <harsh.gupta@...com>
Subject: Re: [PATCH v3 6/8] phy: miphy28lp: Add SSC support for PCIE

Hi Valdis,
Thanks for your remark.

Concerning multiple writing in MIPHY_PLL_SBR_1, the writing of the
first 0 it's to be sure there is no previous request.
Then we take account new setting by writing 0x02.
And then we make it 0 to make sure there is no other pending requests.

I added comments and macro to be more clear (see the code below).


Hi Kishon,

Do you want a new patch set (v4),  or i wait other remarks from you ?


    for (val = 0; val < 2; val++) {
        writeb_relaxed(val, miphy_phy->base + MIPHY_CONF);

        /* Validate Step component */
        writeb_relaxed(0x69, miphy_phy->base + MIPHY_PLL_SBR_3);
        writeb_relaxed(0x21, miphy_phy->base + MIPHY_PLL_SBR_4);

        /* Validate Period component */
        writeb_relaxed(0x3c, miphy_phy->base + MIPHY_PLL_SBR_2);
        writeb_relaxed(0x21, miphy_phy->base + MIPHY_PLL_SBR_4);

        /* Clear any previous request */
        writeb_relaxed(0x00, miphy_phy->base + MIPHY_PLL_SBR_1);

        /* requests the PLL to take in account new parameters */
        writeb_relaxed(SET_NEW_CHANGE, base + MIPHY_PLL_SBR_1);

        /* To be sure there is no other pending requests */
        writeb_relaxed(0x00, miphy_phy->base + MIPHY_PLL_SBR_1);
    }


Best regards

Gabriel.


On 29 September 2014 21:19,  <Valdis.Kletnieks@...edu> wrote:
> On Fri, 26 Sep 2014 10:54:15 +0200, Gabriel FERNANDEZ said:
>> SSC is the technique of modulating the operating frequency of a signal
>> slightly to spread its radiated emissions over a range of frequencies.
>> This reduction in the maximum emission for a given frequency helps meet
>> radiated emission requirements.
>> These settings are applicable for PCIE with Internal clock.
>
>> +             writeb_relaxed(0x69, miphy_phy->base + MIPHY_PLL_SBR_3);
>> +             writeb_relaxed(0x21, miphy_phy->base + MIPHY_PLL_SBR_4);
>> +             writeb_relaxed(0x3c, miphy_phy->base + MIPHY_PLL_SBR_2);
>> +             writeb_relaxed(0x21, miphy_phy->base + MIPHY_PLL_SBR_4);
>> +             writeb_relaxed(0x00, miphy_phy->base + MIPHY_PLL_SBR_1);
>> +             writeb_relaxed(0x02, miphy_phy->base + MIPHY_PLL_SBR_1);
>> +             writeb_relaxed(0x00, miphy_phy->base + MIPHY_PLL_SBR_1);
>
> I'd feel a lot better about all these magic numbers (and the triple write
> to SBR_1) if the Changelog or something referenced where they came from....
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