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SubjectRe: [PATCH] mtd: rawnand: denali: add reset controlling
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Hi Masahiro,

On Tue, 2019-12-10 at 18:14 +0900, Masahiro Yamada wrote:
> According to the Denali User's Guide, this IP has two reset signals.
>
> rst_n: reset most of FFs in the controller core
> reg_rst_n: reset all FFs in the register interface, and in the
> initialization sequence
>
> This commit supports controlling those reset signals, although they
> might be often tied up together in actual SoC integration.
>
> One thing that should be kept in mind is the automated initialization
> sequence (a.k.a. 'bootstrap' process) is kicked off when reg_rst_n is
> deasserted.
>
> When the reset is deasserted, the controller issues a RESET command
> to the chip select 0, and attempts to read out the chip ID, and further
> more, ONFI parameters if it is an ONFI-compliant device. Then, the
> controller sets up the relevant registers based on the detected
> device parameters.
>
> This process is just redundant for Linux because nand_scan_ident()
> probes devices and sets up parameters accordingly. Rather, this hardware
> feature is annoying because it ends up with misdetection due to bugs.
>
> So, commit 0615e7ad5d52 ("mtd: nand: denali: remove Toshiba and Hynix
> specific fixup code") changed the driver to not rely on it.
>
> However, there is no way to prevent it from running. The IP provides
> the 'bootstrap_inhibit_init' port to suppress this sequence, but it is
> usually out of software control, and dependent on SoC implementation.
> As for the Socionext UniPhier platform, LD4 always enables it. For the
> later SoCs, the bootstrap sequence runs depending on the boot mode.
>
> I added usleep_range() to make the driver wait until the sequence
> finishes. Otherwise, the driver would fail to detect the chip due
> to the race between the driver and hardware-controlled sequence.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
>
> .../devicetree/bindings/mtd/denali-nand.txt | 7 ++++
> drivers/mtd/nand/raw/denali_dt.c | 40 ++++++++++++++++++-
> 2 files changed, 46 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/mtd/denali-nand.txt b/Documentation/devicetree/bindings/mtd/denali-nand.txt
> index b32aed1db46d..a48b17fb969a 100644
> --- a/Documentation/devicetree/bindings/mtd/denali-nand.txt
> +++ b/Documentation/devicetree/bindings/mtd/denali-nand.txt
> @@ -14,6 +14,11 @@ Required properties:
> interface clock, and the ECC circuit clock.
> - clock-names: should contain "nand", "nand_x", "ecc"
>
> +Optional properties:
> + - resets: may contain phandles to the controller core reset, the register
> + reset
> + - reset-names: may contain "nand", "reg"
> +
> Sub-nodes:
> Sub-nodes represent available NAND chips.
>
> @@ -46,6 +51,8 @@ nand: nand@ff900000 {
> reg-names = "nand_data", "denali_reg";
> clocks = <&nand_clk>, <&nand_x_clk>, <&nand_ecc_clk>;
> clock-names = "nand", "nand_x", "ecc";
> + resets = <&nand_rst>, <&nand_reg_rst>;
> + reset-names = "nand", "reg";
> interrupts = <0 144 4>;
>
> nand@0 {

According to Documentation/devicetree/bindings/submitting-patches.txt
this part should be a separate patch.

> diff --git a/drivers/mtd/nand/raw/denali_dt.c b/drivers/mtd/nand/raw/denali_dt.c
> index 8b779a899dcf..132bc6cc066c 100644
> --- a/drivers/mtd/nand/raw/denali_dt.c
> +++ b/drivers/mtd/nand/raw/denali_dt.c
> @@ -6,6 +6,7 @@
> */
>
> #include <linux/clk.h>
> +#include <linux/delay.h>
> #include <linux/err.h>
> #include <linux/io.h>
> #include <linux/ioport.h>
> @@ -14,6 +15,7 @@
> #include <linux/of.h>
> #include <linux/of_device.h>
> #include <linux/platform_device.h>
> +#include <linux/reset.h>
>
> #include "denali.h"
>
> @@ -22,6 +24,8 @@ struct denali_dt {
> struct clk *clk; /* core clock */
> struct clk *clk_x; /* bus interface clock */
> struct clk *clk_ecc; /* ECC circuit clock */
> + struct reset_control *rst; /* core reset */
> + struct reset_control *rst_reg; /* register reset */
> };
>
> struct denali_dt_data {
> @@ -151,6 +155,14 @@ static int denali_dt_probe(struct platform_device *pdev)
> if (IS_ERR(dt->clk_ecc))
> return PTR_ERR(dt->clk_ecc);
>
> + dt->rst = devm_reset_control_get_optional_shared(dev, "nand");
> + if (IS_ERR(dt->rst))
> + return PTR_ERR(dt->rst);
> +
> + dt->rst_reg = devm_reset_control_get_optional_shared(dev, "reg");
> + if (IS_ERR(dt->rst_reg))
> + return PTR_ERR(dt->rst_reg);
> +
> ret = clk_prepare_enable(dt->clk);
> if (ret)
> return ret;
> @@ -166,10 +178,30 @@ static int denali_dt_probe(struct platform_device *pdev)
> denali->clk_rate = clk_get_rate(dt->clk);
> denali->clk_x_rate = clk_get_rate(dt->clk_x);
>
> - ret = denali_init(denali);
> + /*
> + * Deassert the register reset, and the core reset in this order.
> + * Deasserting the core reset while the register reset is asserted
> + * will cause unpredictable behavior in the controller.
> + */
> + ret = reset_control_deassert(dt->rst_reg);
> if (ret)
> goto out_disable_clk_ecc;
>
> + ret = reset_control_deassert(dt->rst);
> + if (ret)
> + goto out_assert_rst_reg;
> +
> + /*
> + * When the reset is deasserted, the initialization sequence is kicked
> + * (bootstrap process). This will take a while, and the driver must
> + * wait until it finished in order to avoid unpredictable behavior.
> + */
> + usleep_range(200, 1000);
> +
> + ret = denali_init(denali);
> + if (ret)
> + goto out_assert_rst;
> +
> for_each_child_of_node(dev->of_node, np) {
> ret = denali_dt_chip_init(denali, np);
> if (ret) {
> @@ -184,6 +216,10 @@ static int denali_dt_probe(struct platform_device *pdev)
>
> out_remove_denali:
> denali_remove(denali);
> +out_assert_rst:
> + reset_control_assert(dt->rst);
> +out_assert_rst_reg:
> + reset_control_assert(dt->rst_reg);
> out_disable_clk_ecc:
> clk_disable_unprepare(dt->clk_ecc);
> out_disable_clk_x:
> @@ -199,6 +235,8 @@ static int denali_dt_remove(struct platform_device *pdev)
> struct denali_dt *dt = platform_get_drvdata(pdev);
>
> denali_remove(&dt->controller);
> + reset_control_assert(dt->rst);
> + reset_control_assert(dt->rst_reg);
> clk_disable_unprepare(dt->clk_ecc);
> clk_disable_unprepare(dt->clk_x);
> clk_disable_unprepare(dt->clk);

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>

for the driver part.

regards
Philipp

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