linux-kernel - RE: [PATCH v4 3/3] pinctrl: Add Xilinx ZynqMP pinctrl driver support

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Date:   Tue, 23 Mar 2021 08:08:00 +0000
From:   Sai Krishna Potthuri <lakshmis@...inx.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michal Simek <michals@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        git <git@...inx.com>,
        "saikrishna12468@...il.com" <saikrishna12468@...il.com>
Subject: RE: [PATCH v4 3/3] pinctrl: Add Xilinx ZynqMP pinctrl driver support

Hi Andy Shevchenko,

> -----Original Message-----
> From: Andy Shevchenko <andy.shevchenko@...il.com>
> Sent: Monday, March 22, 2021 10:47 PM
> To: Sai Krishna Potthuri <lakshmis@...inx.com>
> Cc: Linus Walleij <linus.walleij@...aro.org>; Rob Herring
> <robh+dt@...nel.org>; Michal Simek <michals@...inx.com>; Greg Kroah-
> Hartman <gregkh@...uxfoundation.org>; linux-arm Mailing List <linux-arm-
> kernel@...ts.infradead.org>; Linux Kernel Mailing List <linux-
> kernel@...r.kernel.org>; devicetree <devicetree@...r.kernel.org>; open
> list:GPIO SUBSYSTEM <linux-gpio@...r.kernel.org>; git <git@...inx.com>;
> saikrishna12468@...il.com
> Subject: Re: [PATCH v4 3/3] pinctrl: Add Xilinx ZynqMP pinctrl driver support
> 
> On Mon, Mar 22, 2021 at 5:25 PM Sai Krishna Potthuri
> <lakshmis@...inx.com> wrote:
> > > From: Andy Shevchenko <andy.shevchenko@...il.com>
> > > Sent: Friday, March 19, 2021 3:53 PM On Thu, Mar 18, 2021 at 4:42 PM
> > > Sai Krishna Potthuri <lakshmis@...inx.com>
> > > wrote:
> > > > > From: Andy Shevchenko <andy.shevchenko@...il.com>
> > > > > Sent: Wednesday, March 17, 2021 6:26 PM On Wed, Mar 17, 2021 at
> > > > > 10:27 AM Sai Krishna Potthuri
> > > > > <lakshmi.sai.krishna.potthuri@...inx.com> wrote:
> 
> ...
> 
> > > > #include <dt-bindings/pinctrl/pinctrl-zynqmp.h>
> > >
> > > Looking into other drivers with similar includes, shouldn't it go
> > > first in the file before any other linux/* asm/* etc?
> > I see some drivers are including this header before linux/* and some
> > are using after linux/*.
> 
> The rule of thumb is that: more generic headers are going first.
> 
> I consider dt/* ones are more generic than linux/* ones because they are
> covering more than just the Linux kernel.
Ok, I will reorder accordingly.
> 
> ...
> 
> > > > > I'm lost here. What is IO standard exactly? Why it can't be in
> > > > > generic headers?
> > > > It represents LVCMOS 3.3 volts/ LVCMOS 1.8 volts.
> > > > Since this is specific to Xilinx ZynqMP platform, considered to be
> > > > added in the driver file.
> > >
> > > So, why can't we create a couple of bits to represent this voltages
> > > in the generic header and gain usability for others as well?
> > I see some drivers are maintaining the configuration list in the
> > driver file, if the configuration is specific to the driver.
> 
> Yes, my point is that this case doesn't sound too specific to the driver. Many
> pin control buffers (in hardware way of speaking) have properties to be
> different voltage tolerant / produce.
Ok, you want me to proceed with this change or shall we wait for
Linus to comment?
> 
> > We can move this to generic header if it is used by others as well.
> > Ok, will wait for Linus to comment.
> > >
> > > Linus?
> 
> ...
> 
> > > > > > +       ret = zynqmp_pm_pinctrl_request(pin);
> > > > > > +       if (ret) {
> > > > > > +               dev_err(pctldev->dev, "request failed for pin
> > > > > > + %u\n", pin);
> > > > >
> > > > > > +               return -EIO;
> > > > >
> > > > > Why shadowing error code?
> > >
> > > So, any comments on the initial Q?
> > Xilinx low level secure firmware error codes are different from Linux error
> codes.
> > Secure firmware maintains list of error codes (positive values other than
> zero).
> > Hence we return -EIO, if the return value from firmware is non-zero.
> 
> Why the zynqmp_pm_pinctrl_request() can't return codes in Linux error
> code space?
I cross checked with the Xilinx firmware team, firmware driver is now returning
Linux error codes in the latest kernel but while developing the driver it was a
different approach. I will update the driver to simply return the values from
firmware calls.
> 
> > > >>  Since it's the only possible error, why is it not
> > > > > reflected in the kernel doc?
> > > > I will update the kernel doc with the error value for such cases.
> > > > >
> > > > > > +       }
> 
> --
> With Best Regards,
> Andy Shevchenko