linux-kernel - Re: [PATCH 2/6] dt-bindings: clock: add DDR3 standard speed bins.

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Message-ID: <62c4b6f0-e67c-8e25-a129-bf0c06c5157b@collabora.com>
Date:   Thu, 19 Apr 2018 13:30:16 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Heiko Stuebner <heiko@...ech.de>
Cc:     myungjoo.ham@...sung.com, kyungmin.park@...sung.com,
        robh+dt@...nel.org, devicetree@...r.kernel.org,
        linux-pm@...r.kernel.org, dbasehore@...omium.org,
        linux-kernel@...r.kernel.org, dianders@...gle.com,
        groeck@...gle.com, kernel@...labora.com,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/6] dt-bindings: clock: add DDR3 standard speed bins.

Hi Heiko,

On 19/04/18 13:10, Heiko Stuebner wrote:
> Hi Enric,
> 
> Am Donnerstag, 19. April 2018, 12:40:15 CEST schrieb Enric Balletbo i Serra:
>> DDR3 SDRAM Standard (JESD79-3F) defines some standard speed bins for
>> DDR3 memories. The devfreq/rk3399_dmc.txt binding refers to this file
>> which does not exist, so add a ddr.h file with the standard speed bins
>> for DDR3.
>>
>> Fixes: c1ceb8f7c167 (Documentation: bindings: add dt documentation for rk3399 dmc)
>> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
>> ---
>>
>>  include/dt-bindings/clock/ddr.h | 34 +++++++++++++++++++++++++++++++++
>>  1 file changed, 34 insertions(+)
>>  create mode 100644 include/dt-bindings/clock/ddr.h
>>
>> diff --git a/include/dt-bindings/clock/ddr.h b/include/dt-bindings/clock/ddr.h
>> new file mode 100644
>> index 000000000000..506aef7e609e
>> --- /dev/null
>> +++ b/include/dt-bindings/clock/ddr.h
>> @@ -0,0 +1,34 @@
>> +/* SPDX-License-Identifier: (GPL-2.0+ OR MIT) */
>> +
>> +#ifndef DT_BINDINGS_DDR_H
>> +#define DT_BINDINGS_DDR_H
>> +
>> +/* DDR3-800 Standard Speed Bins */
>> +#define DDR3_800D	15
>> +#define DDR3_800E		18
>> +/* DDR3-1066 Standard Speed Bins */
>> +#define DDR3_1066E	18
>> +#define DDR3_1066F	21
>> +#define DDR3_1066G	24
> 
> looking at the mentioned jedec standard, I don't see where these numerical
> values are defined in the standard itself. [I may be blind though]
> 

Damm it. No, you're not blind. I did an horrible mistake adding an old version
of this file. It's wrong, that is supposed to be there is DDR3 table available
in the ATF [1] not this.

        /* 5-5-5 */
	DDR3_800D = 0,
	/* 6-6-6 */
	DDR3_800E = 1,
	/* 6-6-6 */
	DDR3_1066E = 2,
	/* 7-7-7 */
	DDR3_1066F = 3,
        ...

The value is passed directly to the ATF so the above values are the correct.

One question that I have on my mind is if this file should be called as is or if
will be better name as atf-ddr.h or something like that.
ddr.h -> atf-ddr.h

[1]
https://github.com/ARM-software/arm-trusted-firmware/blob/master/plat/rockchip/rk3399/drivers/dram/dram_spec_timing.h

Sorry about that. Guess it's needed a v2 but let's wait a little bit for if more
discussion arises.

Best regards,
  Enric

> Could you explain a bit more where these numerical values are coming from?
> 
> 
> Thanks
> Heiko
>