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

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Sun, 19 Jun 2016 20:41:09 +0800
icenowy@aosc.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@free-electrons.com>:
> > +Philipp
> >
> > On Sun, 19 Jun 2016 19:37:39 +0800
> > Icenowy Zheng <icenowy@aosc.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@aosc.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;
> >>  + }
> >>  + }
> >>  +