[PATCH] pci: pci_mvebu: Add support for reset-gpios

[Pali Rohár]

On Thursday 28 July 2022 17:05:38 Stefan Roese wrote:
> On 28.07.22 15:03, Pali Rohár wrote:
> > Release PERST# signal via GPIO when "reset-gpios" is defined in device tree.
> > 
> > Signed-off-by: Pali Rohár <pali at kernel.org>
> > ---
> >   drivers/pci/pci_mvebu.c | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/pci/pci_mvebu.c b/drivers/pci/pci_mvebu.c
> > index d80f87e0cfc6..269c027db204 100644
> > --- a/drivers/pci/pci_mvebu.c
> > +++ b/drivers/pci/pci_mvebu.c
> > @@ -22,6 +22,7 @@
> >   #include <asm/io.h>
> >   #include <asm/arch/cpu.h>
> >   #include <asm/arch/soc.h>
> > +#include <asm-generic/gpio.h>
> >   #include <linux/bitops.h>
> >   #include <linux/delay.h>
> >   #include <linux/errno.h>
> > @@ -60,6 +61,7 @@ struct mvebu_pcie {
> >   	struct resource mem;
> >   	void __iomem *iobase;
> >   	struct resource io;
> > +	struct gpio_desc reset_gpio;
> >   	u32 intregs;
> >   	u32 port;
> >   	u32 lane;
> > @@ -416,6 +418,14 @@ static int mvebu_pcie_probe(struct udevice *dev)
> >   	struct udevice *ctlr = pci_get_controller(dev);
> >   	struct pci_controller *hose = dev_get_uclass_priv(ctlr);
> >   	u32 reg;
> > +	int ret;
> > +
> > +	/* Request for optional PERST# GPIO */
> > +	ret = gpio_request_by_name(dev, "reset-gpios", 0, &pcie->reset_gpio, GPIOD_IS_OUT);
> > +	if (ret && ret != -ENOENT) {
> > +		printf("%s: unable to request reset-gpios: %d\n", pcie->name, ret);
> > +		return ret;
> > +	}
> >   	/*
> >   	 * Change Class Code of PCI Bridge device to PCI Bridge (0x600400)
> > @@ -537,6 +547,10 @@ static int mvebu_pcie_probe(struct udevice *dev)
> >   	pcie->cfgcache[(PCI_PREF_MEMORY_BASE - 0x10) / 4] =
> >   		PCI_PREF_RANGE_TYPE_64 | (PCI_PREF_RANGE_TYPE_64 << 16);
> > +	/* Release PERST# via GPIO when it was defined */
> > +	if (dm_gpio_is_valid(&pcie->reset_gpio))
> > +		dm_gpio_set_value(&pcie->reset_gpio, 0);
> > +
> 
> So you're only releasing the GPIO (setting to inactive) here. Wouldn't
> it make sense to first use the GPIO (if available via DT) to actually
> reset the PCI device? How is this done in the Kernel driver(s)?
> 
> Thanks,
> Stefan

This is something which I do not know what is the best. Kernel driver
pci-mvebu.c has same logic - just release from reset at startup.