From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: "Wells Lu 呂芳騰" <wells.lu@sunplus.com>
Cc: Wells Lu <wellslutw@gmail.com>,
Linus Walleij <linus.walleij@linaro.org>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Rob Herring <robh+dt@kernel.org>,
devicetree <devicetree@vger.kernel.org>,
linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
"dvorkin@tibbo.com" <dvorkin@tibbo.com>
Subject: Re: [PATCH v5 2/2] pinctrl: Add driver for Sunplus SP7021
Date: Fri, 14 Jan 2022 13:16:43 +0200 [thread overview]
Message-ID: <CAHp75VdTm5T=VGgrqfp+3bLAu4chosirJ2uBeoA5MxvV+FMg_Q@mail.gmail.com> (raw)
In-Reply-To: <b9c1876c9d0f48a3a8d7e091d47fc069@sphcmbx02.sunplus.com.tw>
On Fri, Jan 14, 2022 at 12:55 PM Wells Lu 呂芳騰 <wells.lu@sunplus.com> wrote:
...
> > > > > > > > > + bool "Sunplus SP7021 PinMux and GPIO driver"
> > > > > > > >
> > > > > > > > Why bool and not tristate?
> > > > > > >
> > > > > > > Pinctrl driver is selected by many drivers in SP7021 platform.
> > > > > > > We never build it as a module, but build-in to kernel.
> > > > > > > So we use "bool".
> > > > > > >
> > > > > > > Should we set it to tristate?
> > > > > >
> > > > > > You still haven't answered "why", so I can't tell you.
> > > > >
> > > > > I am puzzled because I think I have answered "why".
> > > >
> > > > Nope. :-)
> > > >
> > > > > Because Pinctrl driver is necessary for all SP7021-based platforms.
> > > >
> > > > "Why?" Why is it necessary (to be built-in)?
> > >
> > > Pinctrl is necessary to be built-in because drivers of boot-device,
> > > like eMMC, SD card, NAND flash, and NOR flash drivers, need it.
> > >
> > > SP7021 supports booting from eMMC, SD card, NAND flash and NOR flash
> > > devices. Their drivers need Pinctrl driver probes in advance.
> >
> > On x86 platforms, for example, booting from eMMC and SD card does not require a pin
> > control driver to be built-in. Why is this requirement for SP platforms?
> Because all pins of boot-device multiplex with GPIO pins.
>
> SP7021 platforms support multi boot devices, including eMMC, SD card,
> SPI-NOR flash, SPI-NAND flash. Each boot device has control-bit(s)
> to enable it.
>
> For example #1, if control-bits of SPI-NOR flash is set 1,
> GPIO 83, 84, 86, 87 are connected to SPI-NOR flash.
> If control-bits of SPI-NOR flash is set 2,
> GPIO 76, 78, 79, 81 are connected to SPI-NOR flash.
> If control-bits of SPI-NOR flash is set 0, no pin is
> connected SPI-NOR flash.
>
> For example #2, if control-bits of eMMC device is set 1,
> GPIO 72, 73, 74, 75, 76, 77, 78, 79, 80, 81 are connected to
> eMMC device.
> If control-bits of eMMC device is set 0, no pin is connected
> eMMC device.
>
> For example #3, if control-bits of SDCard device is set 1,
> GPIO 65, 66, 67, 68, 69, 70 are connected to SD Card device.
> If control-bits of SDCard device is set 0, no pin is connected
> SDCard device.
>
> Note that all pins multiplex with GPIO pins.
>
> Normally, only a boot-device is enabled. All other GPIO pins
> are released for peripherals (controlled by fully-pinmux
> Or group pinmux) or IO processor
Thanks for this detailed picture of the HW configuration.
> Pinctrl driver is responsible for setup the pins.
> If Pinctrl fails to probe, boot-device also fails to probe.
But have you tried to compile it as a module and supply it in the initramfs?
What kernel does in this case it takes address of initramfs from
memory (I believe you have bootloader that capable to setup kernel,
initramfs, command line, and device
tree blob and pass the control to the kernel) at some point, mounts it
and probes the modules that are required to get your boot device
ready.
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2022-01-14 11:17 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-24 7:42 [PATCH v5 0/2] This is a patch series for pinctrl driver of Sunplus SP7021 SoC Wells Lu
2021-12-24 7:42 ` [PATCH v5 1/2] dt-bindings: pinctrl: Add dt-bindings for Sunplus SP7021 Wells Lu
2021-12-25 14:48 ` Rob Herring
2021-12-26 12:44 ` Wells Lu 呂芳騰
2021-12-27 16:02 ` Rob Herring
2021-12-27 16:10 ` Rob Herring
2021-12-27 17:36 ` Wells Lu 呂芳騰
2021-12-24 7:42 ` [PATCH v5 2/2] pinctrl: Add driver " Wells Lu
2021-12-25 15:32 ` Andy Shevchenko
2021-12-28 15:38 ` Wells Lu 呂芳騰
2022-01-10 18:41 ` Andy Shevchenko
2022-01-13 17:04 ` Wells Lu 呂芳騰
2022-01-13 18:04 ` Andy Shevchenko
2022-01-14 2:51 ` Wells Lu 呂芳騰
2022-01-14 9:46 ` Andy Shevchenko
2022-01-14 10:56 ` Wells Lu 呂芳騰
2022-01-14 11:16 ` Andy Shevchenko [this message]
2022-01-14 11:36 ` Wells Lu 呂芳騰
2022-01-10 18:17 ` Wells Lu 呂芳騰
2022-01-10 18:42 ` Andy Shevchenko
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