Date:   Fri, 17 Jul 2020 12:17:57 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Ben Chuang <benchuanggli@...il.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ben Chuang <ben.chuang@...esyslogic.com.tw>,
        Takahiro Akashi <takahiro.akashi@...aro.org>,
        greg.tu@...esyslogic.com.tw
Subject: Re: [RFC PATCH V3 00/21] Add support UHS-II for GL9755

On Fri, 10 Jul 2020 at 13:07, Ben Chuang <benchuanggli@...il.com> wrote:
>
> Summary
> =======
> These patches[1] support UHS-II and fix GL9755 UHS-II compatibility.

First of all, thanks for posting this - and my apologies for not
having the bandwidth to review the earlier versions.

>
> About UHS-II, roughly deal with the following three parts:
> 1) A UHS-II detection and initialization:
> - Host setup to support UHS-II (Section 3.13.1 Host Controller Setup Sequence
>   [2]).
> - Detect a UHS-II I/F (Section 3.13.2 Card Interface Detection Sequence[2]).
> - In step(9) of Section 3.13.2 in [2], UHS-II initialization is include Section
>   3.13.3 UHS-II Card Initialization and Section 3.13.4 UHS-II Setting Register
>   Setup Sequence.
>
> 2) Send Legacy SD command through SD-TRAN
> - Encapsulated SD packets are defined in SD-TRAN in order to ensure Legacy SD
>   compatibility and preserve Legacy SD infrastructures (Section 7.1.1 Packet
>   Types and Format Overview[3]).
> - Host issue a UHS-II CCMD packet or a UHS-II DCMD (Section 3.13.5 UHS-II
>   CCMD Packet issuing and Section 3.13.6 UHS-II DCMD Packet issuing[2]).
>
> 3) UHS-II Interrupt
> - Except for UHS-II error interrupts, most interrupts share the original
>   interrupt registers.

The above points to some specifications, which is good, but what I
really need to be able to do a proper review -  is an explanation of
*what*, *why* and *how* the series implements the UHS-II support.

To be clear, I don't need in-depth details, as that should be
described in each patch's commit message, but I would appreciate an
overall description of the approach you have taken to implement this.

The reason I need this is because UHS-II is a completely new
interface/protocol. If it wasn't because that a UHS-II card is also
required to be backwards compatible with the legacy SD interface, one
could even consider introducing an entirely new subsystem. Not saying
that we should, but just pointing out that the series is not trivial
to review.

That said, I am going to give it a real try to do the review. I will
try to focus on the overall approach, rather than on the details, at
least to start with.

>
> Patch structure
> ===============
> patch#1-#7: for core
> patch#8-#17: for sdhci
> patch#18-#21: for GL9755
>
> Tests
> =====
> Ran 'dd' command to evaluate the performance:
> (SanDisk UHS-II card on GL9755 controller)
>                              Read    Write
> UHS-II disabled (UHS-I): 88.3MB/s 60.7MB/s
> UHS-II enabled         :  206MB/s   80MB/s

I like these comparisons, thanks for sharing!

What UHS-II interface mode does you HW support? FD156, HD312, FD312 FD624?

>
> TODO
> ====
> - replace some define with BIT macro
>
> Reference
> =========
> [1] https://gitlab.com/ben.chuang/linux-uhs2-gl9755.git
> [2] SD Host Controller Simplified Specification 4.20
> [3] UHS-II Simplified Addendum 1.02
>
> Changes in v3 (Jul. 10, 2020)
> * rebased to v5.8-rc4
> * add copyright notice
> * reorganize the patch set and split some commits into smaller ones
> * separate uhs-2 headers from others
> * correct wrong spellings
> * fix most of checkpatch warnings/errors
> * remove all k[cz]alloc() from the code
> * guard sdhci-uhs2 specific code with
>       'if (IS_ENABLED(CONFIG_MMC_SDHCI_UHS2))'
> * make sdhci-uhs2.c as a module
> * trivial changes, including
>   - rename back sdhci-core.c to sdhci.c
>   - allow vendor code to disable uhs2 if v4_mode == 0
>       in __sdhci_add_host()
>   - merge uhs2_power_up() into mmc_power_up()
>   - remove flag_uhs2 from mmc_attach_sd()
>   - add function descriptions to EXPORT'ed functions
>   - other minor code optimization
>
> Changes in v2 (Jan. 9, 2020)
> * rebased to v5.5-rc5
>
> AKASHI Takahiro (15):
>   mmc: core: UHS-II support, modify power-up sequence
>   mmc: core: UHS-II support, skip set_chip_select()
>   mmc: core: UHS-II support, skip TMODE setup in some cases
>   mmc: core: UHS-II support, generate UHS-II SD command packet
>   mmc: core: UHS-II support, set APP_CMD bit if necessary
>   mmc: sdhci: add a kernel configuration for enabling UHS-II support
>   mmc: sdhci: add UHS-II related definitions in headers
>   mmc: sdhci: UHS-II support, dump UHS-II registers
>   mmc: sdhci: UHS-II support, export host operations to core
>   mmc: sdhci: UHS-II support, skip signal_voltage_switch()
>   mmc: sdhci: UHS-II support, handle vdd2 in case of power-off
>   mmc: sdhci: UHS-II support, modify set_power() to handle vdd2
>   mmc: sdhci: UHS-II support, export helper functions to a module
>   mmc: sdhci: UHS-II support, implement operations as a module
>   mmc: core: add post-mmc_attach_sd hook
>
> Ben Chuang (6):
>   mmc: add UHS-II related definitions in public headers
>   mmc: core: UHS-II support, try to select UHS-II interface
>   mmc: sdhci: UHS-II support, add hooks for additional operations
>   mmc: sdhci-uhs2: add pre-detect_init hook
>   mmc: sdhci-uhs2: add post-mmc_attach_sd hook
>   mmc: sdhci-pci-gli: enable UHS-II mode for GL9755
>
>  drivers/mmc/core/Makefile         |   2 +-
>  drivers/mmc/core/block.c          |   7 +-
>  drivers/mmc/core/bus.c            |   5 +-
>  drivers/mmc/core/core.c           | 119 +++-
>  drivers/mmc/core/regulator.c      |  14 +
>  drivers/mmc/core/sd.c             |  32 ++
>  drivers/mmc/core/sd_ops.c         |  12 +
>  drivers/mmc/core/uhs2.c           | 874 ++++++++++++++++++++++++++++++

Nitpick:

I would prefer to prefix any new needed file with sd_*. In this case,
sd_uhs2.c|h.

>  drivers/mmc/core/uhs2.h           |  21 +
>  drivers/mmc/host/Kconfig          |  10 +
>  drivers/mmc/host/Makefile         |   1 +
>  drivers/mmc/host/sdhci-omap.c     |   2 +-
>  drivers/mmc/host/sdhci-pci-core.c |   4 +-
>  drivers/mmc/host/sdhci-pci-gli.c  | 361 +++++++++++-
>  drivers/mmc/host/sdhci-pxav3.c    |   4 +-
>  drivers/mmc/host/sdhci-uhs2.c     | 797 +++++++++++++++++++++++++++
>  drivers/mmc/host/sdhci-uhs2.h     | 215 ++++++++
>  drivers/mmc/host/sdhci-xenon.c    |   4 +-
>  drivers/mmc/host/sdhci.c          | 321 +++++++++--
>  drivers/mmc/host/sdhci.h          | 113 +++-
>  include/linux/mmc/card.h          |   1 +
>  include/linux/mmc/core.h          |   6 +
>  include/linux/mmc/host.h          |  31 ++
>  include/linux/mmc/uhs2.h          | 268 +++++++++
>  24 files changed, 3151 insertions(+), 73 deletions(-)
>  create mode 100644 drivers/mmc/core/uhs2.c
>  create mode 100644 drivers/mmc/core/uhs2.h
>  create mode 100644 drivers/mmc/host/sdhci-uhs2.c
>  create mode 100644 drivers/mmc/host/sdhci-uhs2.h
>  create mode 100644 include/linux/mmc/uhs2.h
>
> --
> 2.27.0
>

Kind regards
Uffe

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