Re: [PATCH 1/2] dt-bindings: nand: meson: add Amlogic NAND controller driver

[Martin Blumenstingl <martin.blumenstingl@googlemail.com>]

Hello Yixun, Hello Liang,

I have a few small comments inline below
additionally I tried to explain the reason behind
"amlogic,mmc-syscon", clkin0 and clkin1 so Rob (or the devicetree
maintainers in general) can give feedback. feel free to correct me
wherever I'm wrong or provide additional notes in case I missed
something!

On Wed, Jun 13, 2018 at 10:17 AM Yixun Lan <yixun.lan@amlogic.com> wrote:
>
> From: Liang Yang <liang.yang@amlogic.com>
>
> Add Amlogic NAND controller dt-bindings for Meson SoC,
> Current this driver support GXBB/GXL/AXG platform.
>
> Signed-off-by: Liang Yang <liang.yang@amlogic.com>
> Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
> ---
>  .../bindings/mtd/amlogic,meson-nand.txt       | 118 ++++++++++++++++++
>  1 file changed, 118 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mtd/amlogic,meson-nand.txt
>
> diff --git a/Documentation/devicetree/bindings/mtd/amlogic,meson-nand.txt b/Documentation/devicetree/bindings/mtd/amlogic,meson-nand.txt
> new file mode 100644
> index 000000000000..eac9f9433d5d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mtd/amlogic,meson-nand.txt
> @@ -0,0 +1,118 @@
> +Amlogic NAND Flash Controller (NFC) for GXBB/GXL/AXG family SoCs
> +
> +This file documents the properties in addition to those available in
> +the MTD NAND bindings.
> +
> +Required properties:
> +- compatible : contains one of:
> +  - "amlogic,meson-gxl-nfc"
> +  - "amlogic,meson-axg-nfc"
the patch description states that GXBB/GXL/AXG are supported
shouldn't you add a compatible string for GXBB as well?

> +- clocks     :
> +       A list of phandle + clock-specifier pairs for the clocks listed
> +       in clock-names.
> +
> +- clock-names: Should contain the following:
> +       "core" - NFC module gate clock
> +       "clkin0" - Parent clock of internal mux
> +       "clkin1" - Other parent clock of internal mux
to give the devicetree maintainers some context on clkin0 and clkin1:

older SoCs (Meson8, Meson8b - not supported by this binding/driver
yet) had a dedicated NAND clock. there neither clkin0 or clkin1 would
be used, instead we just had a "nand" or "interface" clock (I'm not
aware of the actual naming in Amlogic's internal datasheets)

newer SoCs do NOT have a dedicated NAND "interface" clock anymore.
instead they are sharing the clock with the "sd_emmc_c" controller (I
*believe* the reason for this is because sd_emmc_c and the NAND
controller use the same pads on the SoC, pinctrl muxing controls where
these pads are routed -> NAND and sd_emmc_c cannot be used at the same
time, so SoC designers probably decided to re-use the clock)

unfortunately the sd_emmc_c clock is not provided by the "main" clock
controller on these newer SoCs
instead the clock is part of the MMC controller's register space (see
the SD_EMMC_CLOCK register in drivers/mmc/host/meson-gx-mmc.c)
even worse: the SD_EMMC_CLOCK contains more than just clock settings
(bit 25 enables the SDIO interrupt, which is currently not supported
by the meson-gx-mmc driver though)

the SD_EMMC_CLOCK register has a mux (CLK_SRC_MASK) to choose from
clkin0 and clkin1 which are passed here
the "amlogic,mmc-syscon" property is used to get a phandle to the
sd_emmc_c syscon register space
thus there is a bit of code duplication in the MMC and NAND drivers
with this binding (because both need to configure the SD_EMMC_CLOCK
register)

> +
> +- pins     : Select pins which NFC need.
> +- nand_pins: Detail NAND pins information.
> +               nand_pins: nand {
> +                       mux {
> +                               groups = "emmc_nand_d0",
> +                                       "emmc_nand_d1",
> +                                       "emmc_nand_d2",
> +                                       "emmc_nand_d3",
> +                                       "emmc_nand_d4",
> +                                       "emmc_nand_d5",
> +                                       "emmc_nand_d6",
> +                                       "emmc_nand_d7",
> +                                       "nand_ce0",
> +                                       "nand_rb0",
> +                                       "nand_ale",
> +                                       "nand_cle",
> +                                       "nand_wen_clk",
> +                                       "nand_ren_wr";
> +                               function = "nand";
> +                       };
> +               };
> +
> +- amlogic,mmc-syscon   : Required for NAND clocks, it's shared with SD/eMMC
> +                               controller port C
> +
> +Optional children nodes:
> +Children nodes represent the available nand chips.
> +
> +Optional properties:
> +- meson-nand-user-mode :
> +       only set 2 or 16 which mean the way of reading OOB bytes by NFC.
as far as I know vendor specific properties should follow the naming
schema "vendor,purpose"
in this case this would be "amlogic,nand-user-mode"

maybe Rob can comment on this?

> +- meson-nand-ran-mode :
> +       setting 0 or 1, means disable/enable scrambler which keeps the balence
> +       of 0 and 1
I assume 0 and 1 are the only possible values.
to use of_property_read_bool in the driver the property would be either:
- (absent) = scrambler is disabled
- amlogic,nand-enable-scrambler (without any value - also same comment
as above for the value) = scrambler is enabled


Regards
Martin