linux-kernel - Re: [PATCH v10 08/13] drivers: memory: add DMC driver for Exynos5422

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Date:   Fri, 14 Jun 2019 15:40:53 +0200
From:   Lukasz Luba <l.luba@...tner.samsung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, linux-clk@...r.kernel.org,
        mturquette@...libre.com, sboyd@...nel.org,
        Bartłomiej Żołnierkiewicz 
        <b.zolnierkie@...sung.com>, kgene@...nel.org,
        Chanwoo Choi <cw00.choi@...sung.com>,
        kyungmin.park@...sung.com,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        s.nawrocki@...sung.com, myungjoo.ham@...sung.com,
        keescook@...omium.org, tony@...mide.com, jroedel@...e.de,
        treding@...dia.com, digetx@...il.com, gregkh@...uxfoundation.org,
        willy.mh.wolff.ml@...il.com
Subject: Re: [PATCH v10 08/13] drivers: memory: add DMC driver for
 Exynos5422

Hi Krzysztof,

On 6/14/19 2:58 PM, Krzysztof Kozlowski wrote:
> On Fri, 14 Jun 2019 at 11:53, Lukasz Luba <l.luba@...tner.samsung.com> wrote:
>>
>> This patch adds driver for Exynos5422 Dynamic Memory Controller.
>> The driver provides support for dynamic frequency and voltage scaling for
>> DMC and DRAM. It supports changing timings of DRAM running with different
>> frequency. There is also an algorithm to calculate timigns based on
>> memory description provided in DT.
>> The patch also contains needed MAINTAINERS file update.
>>
>> Signed-off-by: Lukasz Luba <l.luba@...tner.samsung.com>
>> ---
>>   MAINTAINERS                             |    8 +
>>   drivers/memory/samsung/Kconfig          |   17 +
>>   drivers/memory/samsung/Makefile         |    1 +
>>   drivers/memory/samsung/exynos5422-dmc.c | 1262 +++++++++++++++++++++++
>>   4 files changed, 1288 insertions(+)
>>   create mode 100644 drivers/memory/samsung/exynos5422-dmc.c
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 57f496cff999..6ffccfd95351 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -3470,6 +3470,14 @@ S:       Maintained
>>   F:     drivers/devfreq/exynos-bus.c
>>   F:     Documentation/devicetree/bindings/devfreq/exynos-bus.txt
>>
>> +DMC FREQUENCY DRIVER FOR SAMSUNG EXYNOS5422
> 
> Eh, more comments from my side.
> "For the hard of thinking, this list is meant to remain in alphabetical order."
OK
> 
>> +M:     Lukasz Luba <l.luba@...tner.samsung.com>
>> +L:     linux-pm@...r.kernel.org
>> +L:     linux-samsung-soc@...r.kernel.org
>> +S:     Maintained
>> +F:     drivers/memory/samsung/exynos5422-dmc.c
>> +F:     Documentation/devicetree/bindings/memory-controllers/exynos5422-dmc.txt
>> +
>>   BUSLOGIC SCSI DRIVER
>>   M:     Khalid Aziz <khalid@...ehiking.org>
>>   L:     linux-scsi@...r.kernel.org
>> diff --git a/drivers/memory/samsung/Kconfig b/drivers/memory/samsung/Kconfig
>> index 79ce7ea58903..c93baa029654 100644
>> --- a/drivers/memory/samsung/Kconfig
>> +++ b/drivers/memory/samsung/Kconfig
>> @@ -5,6 +5,23 @@ config SAMSUNG_MC
>>            Support for the Memory Controller (MC) devices found on
>>            Samsung Exynos SoCs.
>>
>> +config ARM_EXYNOS5422_DMC
> 
> Why you added prefix of ARM to CONFIG think none of other Exynos
> Kconfig options follow such convention (except devfreq).
In the previous versions the driver was in drivers/devfreq/,
that's why they have this prefix.
> 
>> +       tristate "ARM EXYNOS5422 Dynamic Memory Controller driver"
>> +       depends on ARCH_EXYNOS
>> +       select DDR
> 
> In general select should be used only for non-visible symbols and DDR
> is visible. Use depends.
OK
> 
>> +       select PM_DEVFREQ
> 
> This definitely cannot be select. You do not select entire subsystem
> because some similar driver was chosen.
So I will use depends int this case
> 
>> +       select DEVFREQ_GOV_SIMPLE_ONDEMAND
>> +       select DEVFREQ_GOV_USERSPACE
> 
> I think only simple_ondemand is needed. Is userspace governor
> necessary for working? Or actually maybe both could be skipped?
> 
Actually we can skip both governors from here.

>> +       select PM_DEVFREQ_EVENT
> 
> Again, depends.
OK

There are these 4 options which the driver depends on:
         depends on ARCH_EXYNOS
         depends on DDR
         depends on PM_DEVFREQ
         depends on PM_DEVFREQ_EVENT

Should I merged them into one, two lines? like below:
a)
depends on (ARCH_EXYNOS && DDR && PM_DEVFREQ && PM_DEVFREQ_EVENT)
b) grouped into two sets
depends on (ARCH_EXYNOS && DDR)
depends on (PM_DEVFREQ && PM_DEVFREQ_EVENT)
c) grouped by pm_devfreq only
depends on ARCH_EXYNOS
depends on DDR
depends on (PM_DEVFREQ && PM_DEVFREQ_EVENT)

> 
>> +       select PM_OPP
This option can be used here IIUC
>> +       help
>> +         This adds driver for Exynos5422 DMC (Dynamic Memory Controller).
>> +         The driver provides support for Dynamic Voltage and Frequency Scaling in
>> +         DMC and DRAM. It also supports changing timings of DRAM running with
>> +         different frequency. The timings are calculated based on DT memory
>> +         information.
>> +
>> +
>>   if SAMSUNG_MC
> 
> Why this is outside of SAMSUNG_MC?
Good question, I will move it below this 'if' statement.

Regards,
Lukasz
> 
> Best regards,
> Krzysztof
> 
>