Re: [PATCH v3 04/10] PCI: apple: Add initial hardware bring-up

[Marc Zyngier <maz@kernel.org>]

On Mon, 13 Sep 2021 21:48:47 +0100,
"Sven Peter" <sven@svenpeter.dev> wrote:
> 
> 
> 
> On Mon, Sep 13, 2021, at 20:25, Marc Zyngier wrote:
> > From: Alyssa Rosenzweig <alyssa@rosenzweig.io>
> > 
> > Add a minimal driver to bring up the PCIe bus on Apple system-on-chips,
> > particularly the Apple M1. This driver exposes the internal bus used for
> > the USB type-A ports, Ethernet, Wi-Fi, and Bluetooth. Bringing up the
> > radios requires additional drivers beyond what's necessary for PCIe
> > itself.
> > 
> > At this stage, nothing is functionnal.
> > 
> > Co-developed-by: Stan Skowronek <stan@corellium.com>
> > Signed-off-by: Stan Skowronek <stan@corellium.com>
> > Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > Link: https://lore.kernel.org/r/20210816031621.240268-3-alyssa@rosenzweig.io
> > ---
> >  MAINTAINERS                         |   7 +
> >  drivers/pci/controller/Kconfig      |  12 ++
> >  drivers/pci/controller/Makefile     |   1 +
> >  drivers/pci/controller/pcie-apple.c | 243 ++++++++++++++++++++++++++++
> >  4 files changed, 263 insertions(+)
> >  create mode 100644 drivers/pci/controller/pcie-apple.c
> > 
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 813a847e2d64..9905cc48fed9 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -1280,6 +1280,13 @@ S:	Maintained
> >  F:	Documentation/devicetree/bindings/iommu/apple,dart.yaml
> >  F:	drivers/iommu/apple-dart.c
> >  
> > +APPLE PCIE CONTROLLER DRIVER
> > +M:	Alyssa Rosenzweig <alyssa@rosenzweig.io>
> > +M:	Marc Zyngier <maz@kernel.org>
> > +L:	linux-pci@vger.kernel.org
> > +S:	Maintained
> > +F:	drivers/pci/controller/pcie-apple.c
> > +
> >  APPLE SMC DRIVER
> >  M:	Henrik Rydberg <rydberg@bitmath.org>
> >  L:	linux-hwmon@vger.kernel.org
> > diff --git a/drivers/pci/controller/Kconfig b/drivers/pci/controller/Kconfig
> > index 326f7d13024f..814833a8120d 100644
> > --- a/drivers/pci/controller/Kconfig
> > +++ b/drivers/pci/controller/Kconfig
> > @@ -312,6 +312,18 @@ config PCIE_HISI_ERR
> >  	  Say Y here if you want error handling support
> >  	  for the PCIe controller's errors on HiSilicon HIP SoCs
> >  
> > +config PCIE_APPLE
> > +	tristate "Apple PCIe controller"
> > +	depends on ARCH_APPLE || COMPILE_TEST
> > +	depends on OF
> > +	depends on PCI_MSI_IRQ_DOMAIN
> > +	help
> > +	  Say Y here if you want to enable PCIe controller support on Apple
> > +	  system-on-chips, like the Apple M1. This is required for the USB
> > +	  type-A ports, Ethernet, Wi-Fi, and Bluetooth.
> > +
> > +	  If unsure, say Y if you have an Apple Silicon system.
> > +
> >  source "drivers/pci/controller/dwc/Kconfig"
> >  source "drivers/pci/controller/mobiveil/Kconfig"
> >  source "drivers/pci/controller/cadence/Kconfig"
> > diff --git a/drivers/pci/controller/Makefile 
> > b/drivers/pci/controller/Makefile
> > index aaf30b3dcc14..f9d40bad932c 100644
> > --- a/drivers/pci/controller/Makefile
> > +++ b/drivers/pci/controller/Makefile
> > @@ -37,6 +37,7 @@ obj-$(CONFIG_VMD) += vmd.o
> >  obj-$(CONFIG_PCIE_BRCMSTB) += pcie-brcmstb.o
> >  obj-$(CONFIG_PCI_LOONGSON) += pci-loongson.o
> >  obj-$(CONFIG_PCIE_HISI_ERR) += pcie-hisi-error.o
> > +obj-$(CONFIG_PCIE_APPLE) += pcie-apple.o
> >  # pcie-hisi.o quirks are needed even without CONFIG_PCIE_DW
> >  obj-y				+= dwc/
> >  obj-y				+= mobiveil/
> > diff --git a/drivers/pci/controller/pcie-apple.c 
> > b/drivers/pci/controller/pcie-apple.c
> > new file mode 100644
> > index 000000000000..f3c414950a10
> > --- /dev/null
> > +++ b/drivers/pci/controller/pcie-apple.c
> > @@ -0,0 +1,243 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * PCIe host bridge driver for Apple system-on-chips.
> > + *
> > + * The HW is ECAM compliant, so once the controller is initialized,
> > + * the driver mostly deals MSI mapping and handling of per-port
> > + * interrupts (INTx, management and error signals).
> > + *
> > + * Initialization requires enabling power and clocks, along with a
> > + * number of register pokes.
> > + *
> > + * Copyright (C) 2021 Alyssa Rosenzweig <alyssa@rosenzweig.io>
> > + * Copyright (C) 2021 Google LLC
> > + * Copyright (C) 2021 Corellium LLC
> > + * Copyright (C) 2021 Mark Kettenis <kettenis@openbsd.org>
> > + *
> > + * Author: Alyssa Rosenzweig <alyssa@rosenzweig.io>
> > + * Author: Marc Zyngier <maz@kernel.org>
> > + */
> > +
> > [...]
> > +
> > +static inline void rmwl(u32 clr, u32 set, void __iomem *addr)
> > +{
> > +	writel_relaxed((readl_relaxed(addr) & ~clr) | set, addr);
> > +}
> 
> This helper is a bit strange, especially since it's always only used
> with either clr != 0 or set != 0 but never (clr = 0 and set = 0) afaict.
> Maybe create two instead for setting and clearing bits?

That's indeed nicer, and it makes the code more readable.

> 
> > +
> > +static int apple_pcie_setup_port(struct apple_pcie *pcie,
> > +				 struct device_node *np)
> > +{
> > +	struct platform_device *platform = to_platform_device(pcie->dev);
> > +	struct apple_pcie_port *port;
> > +	struct gpio_desc *reset;
> > +	u32 stat, idx;
> > +	int ret;
> > +
> > +	reset = gpiod_get_from_of_node(np, "reset-gpios", 0,
> > +				       GPIOD_OUT_LOW, "#PERST");
> > +	if (IS_ERR(reset))
> > +		return PTR_ERR(reset);
> > +
> > +	port = devm_kzalloc(pcie->dev, sizeof(*port), GFP_KERNEL);
> > +	if (!port)
> > +		return -ENOMEM;
> > +
> > +	ret = of_property_read_u32_index(np, "reg", 0, &idx);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* Use the first reg entry to work out the port index */
> > +	port->idx = idx >> 11;
> > +	port->pcie = pcie;
> > +	port->np = np;
> > +
> > +	port->base = devm_platform_ioremap_resource(platform, port->idx + 2);
> > +	if (IS_ERR(port->base))
> > +		return -ENODEV;
> > +
> > +	rmwl(0, PORT_APPCLK_EN, port + PORT_APPCLK);
> > +
> > +	rmwl(0, PORT_PERST_OFF, port->base + PORT_PERST);
> > +	gpiod_set_value(reset, 1);
> > +
> > +	ret = readl_relaxed_poll_timeout(port->base + PORT_STATUS, stat,
> > +					 stat & PORT_STATUS_READY, 100, 250000);
> > +	if (ret < 0) {
> > +		dev_err(pcie->dev, "port %pOF ready wait timeout\n", np);
> > +		return ret;
> > +	}
> > +
> > +	/* Flush writes and enable the link */
> > +	dma_wmb();
> 
> This is a DMA barrier but there's no DMA you need to order this against
> here. I think you can just drop it.

Indeed, this is all MMIO based, and doesn't refer to anything in
memory. Barrier gone.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.