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From:   Kevin Hilman <khilman@baylibre.com>
To:     Miquel Raynal <miquel.raynal@bootlin.com>
Cc:     Boris Brezillon <boris.brezillon@bootlin.com>,
        Yixun Lan <yixun.lan@amlogic.com>,
        <linux-mtd@lists.infradead.org>,
        Liang Yang <liang.yang@amlogic.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Marek Vasut <marek.vasut@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Jerome Brunet <jbrunet@baylibre.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Carlo Caione <carlo@caione.org>, Rob Herring <robh@kernel.org>,
        Jian Hu <jian.hu@amlogic.com>,
        <linux-amlogic@lists.infradead.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] mtd: rawnand: meson: add support for Amlogic NAND flash controller
Organization: BayLibre
References: <20180613161314.14894-1-yixun.lan@amlogic.com>
        <20180613161314.14894-3-yixun.lan@amlogic.com>
        <20180624213844.2207ca6f@bbrezillon> <7ha7rfiz3c.fsf@baylibre.com>
        <20180628090034.0637a062@xps13>
Date:   Thu, 28 Jun 2018 16:45:53 -0700
In-Reply-To: <20180628090034.0637a062@xps13> (Miquel Raynal's message of "Thu,
        28 Jun 2018 09:00:34 +0200")
Message-ID: <7hr2kqfpam.fsf@baylibre.com>
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Hi Miquel,

Miquel Raynal <miquel.raynal@bootlin.com> writes:

> On Wed, 27 Jun 2018 16:33:43 -0700, Kevin Hilman <khilman@baylibre.com>
> wrote:
>
>> Hi Boris,
>> 
>> Boris Brezillon <boris.brezillon@bootlin.com> writes:
>> 
>> > Hi Yixun,
>> >
>> > On Wed, 13 Jun 2018 16:13:14 +0000
>> > Yixun Lan <yixun.lan@amlogic.com> wrote:
>> >  
>> >> From: Liang Yang <liang.yang@amlogic.com>
>> >> 
>> >> Add initial support for the Amlogic NAND flash controller which found
>> >> in the Meson-GXBB/GXL/AXG SoCs.
>> >> 
>> >> Singed-off-by: Liang Yang <liang.yang@amlogic.com>
>> >> Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
>> >> ---
>> >>  drivers/mtd/nand/raw/Kconfig      |    8 +
>> >>  drivers/mtd/nand/raw/Makefile     |    3 +
>> >>  drivers/mtd/nand/raw/meson_nand.c | 1422 +++++++++++++++++++++++++++++
>> >>  3 files changed, 1433 insertions(+)
>> >>  create mode 100644 drivers/mtd/nand/raw/meson_nand.c  
>> >
>> > Can you run checkpatch.pl --strict and fix the coding style issues?
>> >  
>> >> 
>> >> diff --git a/drivers/mtd/nand/raw/Kconfig b/drivers/mtd/nand/raw/Kconfig
>> >> index 19a2b283fbbe..b3c17a3ca8f4 100644
>> >> --- a/drivers/mtd/nand/raw/Kconfig
>> >> +++ b/drivers/mtd/nand/raw/Kconfig
>> >> @@ -534,4 +534,12 @@ config MTD_NAND_MTK
>> >>  	  Enables support for NAND controller on MTK SoCs.
>> >>  	  This controller is found on mt27xx, mt81xx, mt65xx SoCs.
>> >>  
>> >> +config MTD_NAND_MESON
>> >> +	tristate "Support for NAND flash controller on Amlogic's Meson SoCs"
>> >> +	depends on ARCH_MESON || COMPILE_TEST
>> >> +	select COMMON_CLK_REGMAP_MESON
>> >> +	select MFD_SYSCON
>> >> +	help
>> >> +	  Enables support for NAND controller on Amlogic's Meson SoCs.
>> >> +
>> >>  endif # MTD_NAND
>> >> diff --git a/drivers/mtd/nand/raw/Makefile b/drivers/mtd/nand/raw/Makefile
>> >> index 165b7ef9e9a1..cdf6162f38c3 100644
>> >> --- a/drivers/mtd/nand/raw/Makefile
>> >> +++ b/drivers/mtd/nand/raw/Makefile
>> >> @@ -1,5 +1,7 @@
>> >>  # SPDX-License-Identifier: GPL-2.0
>> >>  
>> >> +ccflags-$(CONFIG_MTD_NAND_MESON) += -I$(srctree)/drivers/clk/meson  
>> >
>> > Please don't do that. If you need to expose common regs, put them
>> > in include/linux/soc/meson/. I'm also not sure why you need to access
>> > the clk regs directly. Why can't you expose the MMC/NAND clk as a clk
>> > provider whose driver would be placed in drivers/clk and which would use
>> > the mmc syscon. This way the same clk driver could be used for both
>> > MMC and NAND clk indifferently, and the NAND driver would be much
>> > simpler.  
>> 
>> [...]
>> 
>> >> +
>> >> +	return 0;
>> >> +}
>> >> +
>> >> +static const char * sd_emmc_ext_clk0_parent_names[MUX_CLK_NUM_PARENTS];
>> >> +
>> >> +static struct clk_regmap sd_emmc_c_ext_clk0_sel = {
>> >> +	.data = &(struct clk_regmap_mux_data){
>> >> +		.offset = SD_EMMC_CLOCK,
>> >> +		.mask = 0x3,
>> >> +		.shift = 6,
>> >> +	},
>> >> +	.hw.init = &(struct clk_init_data) {
>> >> +		.name = "sd_emmc_c_nand_clk_mux",
>> >> +		.ops = &clk_regmap_mux_ops,
>> >> +		.parent_names = sd_emmc_ext_clk0_parent_names,
>> >> +		.num_parents = ARRAY_SIZE(sd_emmc_ext_clk0_parent_names),
>> >> +		.flags = CLK_SET_RATE_PARENT,
>> >> +	},
>> >> +};
>> >> +
>> >> +static struct clk_regmap sd_emmc_c_ext_clk0_div = {
>> >> +	.data = &(struct clk_regmap_div_data){
>> >> +		.offset = SD_EMMC_CLOCK,
>> >> +		.shift = 0,
>> >> +		.width = 6,
>> >> +		.flags = CLK_DIVIDER_ROUND_CLOSEST | CLK_DIVIDER_ONE_BASED,
>> >> +	},
>> >> +	.hw.init = &(struct clk_init_data) {
>> >> +		.name = "sd_emmc_c_nand_clk_div",
>> >> +		.ops = &clk_regmap_divider_ops,
>> >> +		.parent_names = (const char *[]){ "sd_emmc_c_nand_clk_mux" },
>> >> +		.num_parents = 1,
>> >> +		.flags = CLK_SET_RATE_PARENT,
>> >> +	},
>> >> +};
>> >> +
>> >> +static int meson_nfc_clk_init(struct meson_nfc *nfc)
>> >> +{
>> >> +	struct clk_regmap *mux = &sd_emmc_c_ext_clk0_sel;
>> >> +	struct clk_regmap *div = &sd_emmc_c_ext_clk0_div;
>> >> +	struct clk *clk;
>> >> +	int i, ret;
>> >> +
>> >> +	/* request core clock */
>> >> +	nfc->core_clk = devm_clk_get(nfc->dev, "core");
>> >> +	if (IS_ERR(nfc->core_clk)) {
>> >> +		dev_err(nfc->dev, "failed to get core clk\n");
>> >> +		return PTR_ERR(nfc->core_clk);
>> >> +	}
>> >> +
>> >> +	/* init SD_EMMC_CLOCK to sane defaults w/min clock rate */
>> >> +	regmap_update_bits(nfc->reg_clk, 0,
>> >> +			CLK_SELECT_NAND | CLK_ALWAYS_ON | CLK_DIV_MASK,
>> >> +			CLK_SELECT_NAND | CLK_ALWAYS_ON | CLK_DIV_MASK);
>> >> +
>> >> +	/* get the mux parents */
>> >> +	for (i = 0; i < MUX_CLK_NUM_PARENTS; i++) {
>> >> +		char name[16];
>> >> +
>> >> +		snprintf(name, sizeof(name), "clkin%d", i);
>> >> +		clk = devm_clk_get(nfc->dev, name);
>> >> +		if (IS_ERR(clk)) {
>> >> +			if (clk != ERR_PTR(-EPROBE_DEFER))
>> >> +				dev_err(nfc->dev, "Missing clock %s\n", name);
>> >> +			return PTR_ERR(clk);
>> >> +		}
>> >> +
>> >> +		sd_emmc_ext_clk0_parent_names[i] = __clk_get_name(clk);
>> >> +	}
>> >> +
>> >> +	mux->map = nfc->reg_clk;
>> >> +	clk = devm_clk_register(nfc->dev, &mux->hw);
>> >> +	if (WARN_ON(IS_ERR(clk)))
>> >> +		return PTR_ERR(clk);
>> >> +
>> >> +	div->map = nfc->reg_clk;
>> >> +	nfc->device_clk = devm_clk_register(nfc->dev, &div->hw);
>> >> +	if (WARN_ON(IS_ERR(nfc->device_clk)))
>> >> +		return PTR_ERR(nfc->device_clk);
>> >> +
>> >> +	ret = clk_prepare_enable(nfc->core_clk);
>> >> +	if (ret) {
>> >> +		dev_err(nfc->dev, "failed to enable core clk\n");
>> >> +		return ret;
>> >> +	}
>> >> +
>> >> +	ret = clk_prepare_enable(nfc->device_clk);
>> >> +	if (ret) {
>> >> +		dev_err(nfc->dev, "failed to enable device clk\n");
>> >> +		clk_disable_unprepare(nfc->core_clk);
>> >> +		return ret;
>> >> +	}
>> >> +
>> >> +	return 0;
>> >> +}  
>> >
>> >
>> > As said above, I don't like having a clk driver here, especially since
>> > the registers you're accessing are not part of the NAND controller
>> > registers. Please try to create a driver in drivers/clk/ for that.  
>> 
>> We went back and forth on this one on some off-list reviews.
>> 
>> Had we known that the NAND controller was (re)using the clock registers
>> internal to the MMC IP block from the beginning, we would have written a
>> clock provider in drivers/clk for this, and shared it.
>> 
>> However, when I wrote the MMC driver[1] (already upstream) along with
>> the bindings[2], we did not fathom that the internal mux and divider
>> would be "borrowed" by another device. :(
>> 
>> We only recently found out that the NAND controller "borrows" one of the
>> MMC clocks, whose registers are inside the MMC range.  Taking the clock
>> out of the MMC driver and into its own clock-provider implies redoing
>> the MMC driver, as well as its bindings, which we wanted to avoid
>> (especially the binding changes.)
>> 
>> We (I can take the blame) decided that since the MMC and NAND are
>> mutually exclusive (they also share pins), that allowing NAND to reuse
>> the MMC range would be a good compromise.  The DT still accurately
>> describes the hardware, but we don't have to throw a large wrench into
>> the DT bindings just for a newly discovered shared clock.
>> 
>> I agree, it's not the prettiest thing, but when we cannot know the full
>> details of the hardware when we start, sometimes we end up in a bit of a
>> mess that requires some compromise.
>
> I totally understand your situation but as MMC and NAND are mutually
> exclusive, how is this a problem to have a dedicated clock driver used
> only by the NAND controller (as maybe a first step)? I mean, if you
> don't change the MMC bindings, then the MMC driver will still use its
> own 'local' clock driver, right?

Yeah, I think you're right.  That would work too.

> I don't know if you can have two nodes reserving the same address
> range though.

You can, but it's a race who gets to claim the region.

You'd have to have the new clock-controler disabled by default, and have
any boards that use the NAND disable the MMC and enable the clock
controller node.

But I think that should work.

Yixun, can you give this approach a try?

Kevin