linux-kernel - Re: [PATCH 2/2] mtd: nand: sunxi: add reset line support

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Message-ID: <20160619151619.4edc64f6@bbrezillon>
Date:	Sun, 19 Jun 2016 15:16:19 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	icenowy@...c.xyz
Cc:	"maxime.ripard@...e-electrons.com" <maxime.ripard@...e-electrons.com>,
	"wens@...e.org" <wens@...e.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"richard@....at" <richard@....at>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"computersforpeace@...il.com" <computersforpeace@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-sunxi@...glegroups.com" <linux-sunxi@...glegroups.com>,
	Philipp Zabel <p.zabel@...gutronix.de>
Subject: Re: [PATCH 2/2] mtd: nand: sunxi: add reset line support

On Sun, 19 Jun 2016 21:11:00 +0800
icenowy@...c.xyz wrote:

> Then I will soon make the v2 patch set, with the error detection part fixed.
> 
> But why does sunxi-mmc check only EPROBE_DEFER?

I guess someone had a probe-dependency problem and fixed this case but
ignored all the possible errors. But there may be other reasons for
devm_reset_control_get_optional() to fail. The only one that is really
reflecting that the reset line is not defined in the DT is -ENOENT.

> 
> 19.06.2016, 20:53, "Boris Brezillon" <boris.brezillon@...e-electrons.com>:
> > On Sun, 19 Jun 2016 20:41:09 +0800
> > icenowy@...c.xyz wrote:
> >  
> >>  To be honest, I copied them from sunxi-mmc.c.
> >>
> >>  What function should be chosen better?  
> >
> > You did the right thing (except for the error detection part). My
> > question was addressed to Philipp (the reset subsystem maintainer).
> >  
> >>  19.06.2016, 20:06, "Boris Brezillon" <boris.brezillon@...e-electrons.com>:  
> >>  > +Philipp
> >>  >
> >>  > On Sun, 19 Jun 2016 19:37:39 +0800
> >>  > Icenowy Zheng <icenowy@...c.xyz> wrote:
> >>  >  
> >>  >>  The NAND controller on some sun8i chips needs its reset line to be deasserted
> >>  >>  before they can enter working state. This commit added the reset line process
> >>  >>  to the driver.
> >>  >>
> >>  >>  Signed-off-by: Icenowy Zheng <icenowy@...c.xyz>
> >>  >>  ---
> >>  >>   drivers/mtd/nand/sunxi_nand.c | 14 ++++++++++++++
> >>  >>   1 file changed, 14 insertions(+)
> >>  >>
> >>  >>  diff --git a/drivers/mtd/nand/sunxi_nand.c b/drivers/mtd/nand/sunxi_nand.c
> >>  >>  index a83a690..1502748 100644
> >>  >>  --- a/drivers/mtd/nand/sunxi_nand.c
> >>  >>  +++ b/drivers/mtd/nand/sunxi_nand.c
> >>  >>  @@ -39,6 +39,7 @@
> >>  >>   #include <linux/gpio.h>
> >>  >>   #include <linux/interrupt.h>
> >>  >>   #include <linux/iopoll.h>
> >>  >>  +#include <linux/reset.h>
> >>  >>
> >>  >>   #define NFC_REG_CTL 0x0000
> >>  >>   #define NFC_REG_ST 0x0004
> >>  >>  @@ -269,6 +270,7 @@ struct sunxi_nfc {
> >>  >>           void __iomem *regs;
> >>  >>           struct clk *ahb_clk;
> >>  >>           struct clk *mod_clk;
> >>  >>  + struct reset_control *reset;
> >>  >>           unsigned long assigned_cs;
> >>  >>           unsigned long clk_rate;
> >>  >>           struct list_head chips;
> >>  >>  @@ -1871,6 +1873,18 @@ static int sunxi_nfc_probe(struct platform_device *pdev)
> >>  >>           if (ret)
> >>  >>                   goto out_ahb_clk_unprepare;
> >>  >>
> >>  >>  + nfc->reset = devm_reset_control_get_optional(dev, "ahb");
> >>  >>  + if (PTR_ERR(nfc->reset) == -EPROBE_DEFER)
> >>  >>  + return PTR_ERR(nfc->reset);  
> >>  >
> >>  > Actually you should test for != -ENOENT, because all error codes except
> >>  > this one should stop the ->probe().
> >>  >
> >>  > BTW, this devm_reset_control_get_optional() is really weird. While most
> >>  > _optional() methods return NULL when the element is not defined in the
> >>  > DT, this one returns -ENOTENT, which makes it impossible to
> >>  > differentiate a real error from a undefined reset line (which is a
> >>  > valid case for _optional()).
> >>  >
> >>  > Philipp, is there a good reason for doing that?
> >>  >  
> >>  >>  +
> >>  >>  + if (!IS_ERR(nfc->reset)) {
> >>  >>  + ret = reset_control_deassert(nfc->reset);
> >>  >>  + if (ret) {
> >>  >>  + dev_err(dev, "reset err %d\n", ret);
> >>  >>  + goto out_mod_clk_unprepare;
> >>  >>  + }
> >>  >>  + }
> >>  >>  +