linux-kernel - Re: [PATCH v2] PCI: apple: Follow the PCIe specifications when resetting the port

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Message-ID: <20211123122719.lput7rmn7qr5wkrj@pali>
Date:   Tue, 23 Nov 2021 13:27:19 +0100
From:   Pali Rohár <pali@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Mark Kettenis <mark.kettenis@...all.nl>, luca@...aceresoli.net,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pci@...r.kernel.org, kernel-team@...roid.com,
        alyssa@...enzweig.io, lorenzo.pieralisi@....com,
        bhelgaas@...gle.com, joey.gouly@....com
Subject: Re: [PATCH v2] PCI: apple: Follow the PCIe specifications when
 resetting the port

On Tuesday 23 November 2021 12:24:10 Marc Zyngier wrote:
> On Mon, 22 Nov 2021 21:50:48 +0000,
> Mark Kettenis <mark.kettenis@...all.nl> wrote:
> > 
> > > Date: Mon, 22 Nov 2021 14:43:37 +0000
> > > From: Marc Zyngier <maz@...nel.org>
> > > 
> > > On Mon, 22 Nov 2021 12:03:47 +0000,
> > > Pali Rohár <pali@...nel.org> wrote:
> > > > 
> > > > On Monday 22 November 2021 10:41:56 Marc Zyngier wrote:
> > > > > While the Apple PCIe driver works correctly when directly booted
> > > > > from the firmware, it fails to initialise when the kernel is booted
> > > > > from a bootloader using PCIe such as u-boot.
> > > > > 
> > > > > That's beacuse we're missing a proper reset of the port (we only
> > > > > clear the reset, but never assert it).
> > > > > 
> > > > > The PCIe spec requirements are two-fold:
> > > > > 
> > > > > - #PERST must be asserted before setting up the clocks, and
> > > > >   stay asserted for at least 100us (Tperst-clk).
> > > > > 
> > > > > - Once #PERST is deasserted, the OS must wait for at least 100ms
> > > > >   "from the end of a Conventional Reset" before we can start talking
> > > > >   to the devices
> > > > > 
> > > > > Implementing this results in a booting system.
> > > > > 
> > > > > Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up")
> > > > > Signed-off-by: Marc Zyngier <maz@...nel.org>
> > > > > Cc: Alyssa Rosenzweig <alyssa@...enzweig.io>
> > > > > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > > > > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > > > > Cc: Pali Rohár <pali@...nel.org>
> > > > 
> > > > Looks good, but see comment below.
> > > > 
> > > > Acked-by: Pali Rohár <pali@...nel.org>
> > > 
> > > Thanks for that.
> > > 
> > > > 
> > > > > ---
> > > > >  drivers/pci/controller/pcie-apple.c | 10 ++++++++++
> > > > >  1 file changed, 10 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> > > > > index 1bf4d75b61be..957960a733c4 100644
> > > > > --- a/drivers/pci/controller/pcie-apple.c
> > > > > +++ b/drivers/pci/controller/pcie-apple.c
> > > > > @@ -539,13 +539,23 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie,
> > > > >  
> > > > >  	rmw_set(PORT_APPCLK_EN, port->base + PORT_APPCLK);
> > > > >  
> > > > > +	/* Engage #PERST before setting up the clock */
> > > > > +	gpiod_set_value(reset, 0);
> > > > > +
> > > > >  	ret = apple_pcie_setup_refclk(pcie, port);
> > > > >  	if (ret < 0)
> > > > >  		return ret;
> > > > >  
> > > > > +	/* The minimal Tperst-clk value is 100us (PCIe CMS r2.0, 2.6.2) */
> > > > > +	usleep_range(100, 200);
> > > > > +
> > > > > +	/* Deassert #PERST */
> > > > >  	rmw_set(PORT_PERST_OFF, port->base + PORT_PERST);
> > > > >  	gpiod_set_value(reset, 1);
> > > > 
> > > > + Luca
> > > > 
> > > > Just one comment. PERST# (PCIe Reset) is active-low signal. De-asserting
> > > > means to really set value to 1.
> > > > 
> > > > But there was a discussion that de-asserting should be done by call:
> > > >   gpiod_set_value(reset, 0);
> > > > 
> > > > https://lore.kernel.org/linux-pci/51be082a-ff10-8a19-5648-f279aabcac51@lucaceresoli.net/
> > > > 
> > > > Could we make this new pcie-apple.c driver to use gpiod_set_value(reset, 0)
> > > > for de-asserting, like in other drivers?
> > > 
> > > I guess it depends whether you care about the assertion or the signal
> > > itself. I think we may have a bug in the way the GPIOs are handled at
> > > the moment, as it makes no difference whether I register the GPIO are
> > > active high or active low...
> > 
> > That's unfortunate.  But maybe that's an opportunity to fix the
> > devicetree to use GPIO_ACTIVE_LOW for these GPIOs?
> 
> Indeed. The following hack does the right thing, and I can then
> reverse the polarity of the reset in the Linux driver. Of course, it
> breaks u-boot at the same time (and I suspect OpenBSD would be equally
> affected).

U-Boot has its own copy of DTS files, right? So it can be fixed in
U-Boot driver together with U-Boot DTS file at the same time.

> So if we are going down that road, we may need a flag day where all
> the moving parts change. I don't really mind not being able to boot
> older kernels, but this goes beyond Linux at this point.
> 
> Thanks,
> 
> 	M.
> 
> diff --git a/arch/arm64/boot/dts/apple/t8103.dtsi b/arch/arm64/boot/dts/apple/t8103.dtsi
> index d2e9afde3729..cad1ab920304 100644
> --- a/arch/arm64/boot/dts/apple/t8103.dtsi
> +++ b/arch/arm64/boot/dts/apple/t8103.dtsi
> @@ -10,6 +10,7 @@
>  #include <dt-bindings/interrupt-controller/apple-aic.h>
>  #include <dt-bindings/interrupt-controller/irq.h>
>  #include <dt-bindings/pinctrl/apple.h>
> +#include <dt-bindings/gpio/gpio.h>
>  
>  / {
>  	compatible = "apple,t8103", "apple,arm-platform";
> @@ -293,7 +294,7 @@ pcie0: pcie@...000000 {
>  			port00: pci@0,0 {
>  				device_type = "pci";
>  				reg = <0x0 0x0 0x0 0x0 0x0>;
> -				reset-gpios = <&pinctrl_ap 152 0>;
> +				reset-gpios = <&pinctrl_ap 152 GPIO_ACTIVE_LOW>;
>  				max-link-speed = <2>;
>  
>  				#address-cells = <3>;
> @@ -313,7 +314,7 @@ port00: pci@0,0 {
>  			port01: pci@1,0 {
>  				device_type = "pci";
>  				reg = <0x800 0x0 0x0 0x0 0x0>;
> -				reset-gpios = <&pinctrl_ap 153 0>;
> +				reset-gpios = <&pinctrl_ap 153 GPIO_ACTIVE_LOW>;
>  				max-link-speed = <2>;
>  
>  				#address-cells = <3>;
> @@ -333,7 +334,7 @@ port01: pci@1,0 {
>  			port02: pci@2,0 {
>  				device_type = "pci";
>  				reg = <0x1000 0x0 0x0 0x0 0x0>;
> -				reset-gpios = <&pinctrl_ap 33 0>;
> +				reset-gpios = <&pinctrl_ap 33 GPIO_ACTIVE_LOW>;
>  				max-link-speed = <1>;
>  
>  				#address-cells = <3>;
> 
> -- 
> Without deviation from the norm, progress is not possible.