[RFC 0/2] Add support for Meson MX "SDIO" MMC driver

Wed May 24 13:37:40 PDT 2017

Hi Ulf,

On Thu, May 11, 2017 at 10:44 PM, Martin Blumenstingl
<martin.blumenstingl at googlemail.com> wrote:
> Hi Ulf,
>
> On Thu, May 11, 2017 at 11:39 AM, Ulf Hansson <ulf.hansson at linaro.org> wrote:
>> On 10 May 2017 at 21:22, Martin Blumenstingl
>> <martin.blumenstingl at googlemail.com> wrote:
>>> Hi Ulf,
>>>
>>> On Wed, May 10, 2017 at 10:44 AM, Ulf Hansson <ulf.hansson at linaro.org> wrote:
>>>> On 6 May 2017 at 19:18, Martin Blumenstingl
>>>> <martin.blumenstingl at googlemail.com> wrote:
>>>>> This is the successor to Carlo Caione's "Add support for Amlogic Meson
>>>>> MMC driver" series (v5) from [0].
>>>>>
>>>>> I would like you to specifically review:
>>>>> - whether I've (ab)used the MMC framework properly (as this is my first
>>>>>   "larger" contribution to an MMC driver)
>>>>
>>>> I take a look soonish.
>>> thank you!
>>>
>>>>> - I think I have improved the locking compared to Carlo's version,
>>>>>   however I'd still like feedback on whether this looks sane now or if I
>>>>>   can improve that even further
>>>>>
>>>>> (notable) changes since Carlo's latest version are:
>>>>> - renamed the driver to meson-mx-sdio (Amlogic's reference kernel calls
>>>>>   the driver "aml_sdio" as there is a second MMC controller in these SoCs
>>>>>   which they call the "SDHC controller"). do the same with our driver to
>>>>
>>>> I don't like to renaming drivers, just because there are a reference
>>>> kernel using a different name.
>>>>
>>>> What's is really the difference between controllers? Why do they have
>>>> two variants?
>>> the driver from this thread is for the "SDSC/SDHC/SDXC card and SDIO
>>> interface with 1-bit and 4-bit data bus width supporting spec version
>>> 2.x/3.x/4.x DS/HS modes up to UHS-I SDR50" (quote taken from the S805
>>> datasheet: [0])
>>> the "other" controller is an "eMMC and MMC card interface with
>>> 1/4/8-bit data bus width supporting spec version 4.4x/4.5x HS200 (up
>>> to 100MHz clock), compatible with standard iNAND interface" (again,
>>> quote taken from the S805 datasheet: [0])
>>>
>>>>
>>>> Can they be managed by the same driver?
>>>>
>>>>>   avoid confusion once we add support for the second controller (which uses
>>>>>   a completely different register layout)
>>>>
>>>> Besides that, do they behave differently in some other way?
>>> both drivers/controllers have a totally different register layout - I
>>> don't see any way how they both could be handled by one driver (the
>>> registers for the controllers from this series are not part of the
>>> documentation, but the registers from the 8-bit capable controller
>>> are, see page 76 and following from the S805 datasheet: [0])
>>
>> Okay, I am starting to understand. :-)
> good to hear that my explanation made (at least some) sense!
>
>> The spec in section 13 describes a controller supporting "MMC/SD/SDIO"
>> cards. However, there is yet another controller which @subject series
>> implement support for.
>> You don't happen to have a public datasheet for this controller as
>> well? If not, never mind.
> unfortunately the controller from @subject does not show up in any of
> the public datasheets, but we have a header file from Amlogic which
> documents it just as well as the datasheet (probably) would: [0]
>
>> Then, meson actually have three different MMC/SD/SDIO controllers, the
>> one in the S805 spec, the one supported by the recently up-streamed
>> meson-gx-mmc.c driver - and the one being supported in this series.
>> Right? And all of them are completely separate and non-compatible?
> yes, unfortunately it seems that there are three different MMC
> controller IP blocks from Amlogic
>
> let me explain this a bit more in detail:
> the code-names of the newer (64-bit) SoCs all start with GX (GXBB,
> GXL, GXM), so we call these "Meson GX".
> the code-names of the older (32-bit) SoCs (at least the ones which are
> not too old) all start with Meson X (where X is a number: Meson6,
> Meson8, Meson8b and Meson8m2), Amlogic's vendor code sometimes calls
> these "MX" (or Meson MX)
>
> the MMC IP blocks in Meson GX SoCs are easy: the same IP block is
> embedded three times -> the driver for this is meson-gx-mmc.c (already
> upstream)
> the MMC IP blocks in Meson MX SoCs are more complicated: 1x 1/4-bit
> which will be handled by the driver from @subject (meson-mx-sdio.c)
> and 1x 1/4/8-bit for which there is only the vendor driver (plus the
> description in the S805 datasheet) available.
>
> so it looks like the older Meson MX SoCs may end up with two different
> drivers, while there's a third driver (for a totally different IP
> block) for the newer Meson GX SoCs.
>
> [snip]
>>>>> - use the common clock framework internally for managing the MMC clock
>>>>>   (there is a fixed-factor clock in the controller which takes clk81 as
>>>>>    input and divides it's clock by two and a divider clock which takes
>>>>>    the result from the fixed-factor clock as input)
>>>>> - support the regulators provided by the MMC framework
>>>>> - support for GPIO-based card-detection and read-only-detection through
>>>>>   the MMC framework
>>>>> - use of the <linux/bitfield.h> FIELD_PREP and FIELD_GET macros where it
>>>>>   make sense (and thus the code easier to read)
>>>>> - re-worked locking (based on the locking in dw_mmc as that also provides
>>>>>   multiple "MMC slots")
>>>>
>>>> Lots of changes!
>>>>
>>>> Before even start to review (or someone else), you really need to make
>>>> this review-able.
>>>>
>>>> So, please, one change per patch - and make sure to write good
>>>> changelogs. Then I can start to review.
>>> from the mainline tree's perspective this is a new driver:
>>
>> Yes, I get it now.
>>
>> I first thought this series was related to the recently up-streamed
>> meson-gx-mmc.c driver. Apologize for my ignorance.
> should I put some more context/details in the description (maybe
> something like: "this is a new driver/binding because the Meson MX
> SoCs use a different IP block than the Meson GX SoCs (the IP block
> from the latter is already supported by the meson-gx-mmc driver)"?
>
>>> Carlo (the original author) initially sent this driver for review more
>>> than 14 months ago. unfortunately it was never merged since you
>>> spotted some issues while reviewing that code, see [1].
>>
>> Yes, I recall that now.
> the 14 month delay was one of the reasons why I decided to re-post it
> only after all features were implemented
>
>>> I would have sent smaller patches for a driver which is already in mainline.
>>
>> Right.
>>
>>>
>>> I also wanted to avoid extra complexity for the internal mux if it was
>>> added later on (if we want to avoid breaking devicetree backwards
>>> compatibility then the driver would have to support both: parsing from
>>> the mmc node directly and parsing child "slot" nodes). we won't have
>>> to change the DT bindings when the first version that will be
>>> mainlined already has support for the mux
>>>
>>> please let me know if there's anything I can do to make the code
>>> easier to review.
>>
>> No worries, let me have a look as is!
> okay, perfect! just take your time and let me know what needs to be changed.
I know that you're probably very busy, but I will still ask: did you
have time to look into this series yet (or do you have any ETA)?

Thank you!
Regards,
Martin