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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Wed, 11 Dec 2019 14:33:07 +0900
Message-ID: <CAK7LNAQnuR0fv6Nv5y=GxHxv8nhDB5K32TyG4G-WyOtJqyh0mg@mail.gmail.com>
Subject: Re: [PATCH] mtd: rawnand: denali: add reset controlling
To:     "Tan, Ley Foon" <ley.foon.tan@intel.com>
Cc:     "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
        Dinh Nguyen <dinguyen@kernel.org>, Marek Vasut <marex@denx.de>,
        Mark Rutland <mark.rutland@arm.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Richard Weinberger <richard@nod.at>,
        Rob Herring <robh+dt@kernel.org>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Wed, Dec 11, 2019 at 2:23 PM Tan, Ley Foon <ley.foon.tan@intel.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Masahiro Yamada <yamada.masahiro@socionext.com>
> > Sent: Tuesday, December 10, 2019 5:15 PM
> > To: linux-mtd@lists.infradead.org
> > Cc: Dinh Nguyen <dinguyen@kernel.org>; Marek Vasut <marex@denx.de>;
> > Tan, Ley Foon <ley.foon.tan@intel.com>; Masahiro Yamada
> > <yamada.masahiro@socionext.com>; Mark Rutland
> > <mark.rutland@arm.com>; Miquel Raynal <miquel.raynal@bootlin.com>;
> > Philipp Zabel <p.zabel@pengutronix.de>; Richard Weinberger
> > <richard@nod.at>; Rob Herring <robh+dt@kernel.org>; Vignesh
> > Raghavendra <vigneshr@ti.com>; devicetree@vger.kernel.org; linux-
> > kernel@vger.kernel.org
> > Subject: [PATCH] mtd: rawnand: denali: add reset controlling
> >
> > 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 {
> > 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);
> Will it trigger error if dts doesn't have "nand" or "reg" for reset-name?
> SOCFPGA dts doesn't have this.


No.
These are optional resets.

If they are not found in DT,
the driver will skip the reset controlling.

Of course, you can add them to your DT later
if you want the driver to take care of the resets.


Best Regards
Masahiro Yamada