linux-kernel - Re: [PATCH 2/4] MIPS: pci: Add driver for MT7621 PCIe controller

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Date:   Mon, 31 May 2021 15:14:31 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Sergio Paracuellos <sergio.paracuellos@...il.com>
Cc:     linux-mips@...r.kernel.org, tsbogend@...ha.franken.de,
        devicetree@...r.kernel.org, matthias.bgg@...il.com,
        john@...ozen.org, bhelgaas@...gle.com, robh+dt@...nel.org,
        linux-staging@...ts.linux.dev, gregkh@...uxfoundation.org,
        neil@...wn.name, ilya.lipnitskiy@...il.com,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 2/4] MIPS: pci: Add driver for MT7621 PCIe controller

On Saturday 15 May 2021 14:40:53 Sergio Paracuellos wrote:
> This patch adds a driver for the PCIe controller of MT7621 SoC.
> 
> Signed-off-by: Sergio Paracuellos <sergio.paracuellos@...il.com>
> ---
>  arch/mips/pci/Makefile     |   1 +
>  arch/mips/pci/pci-mt7621.c | 624 +++++++++++++++++++++++++++++++++++++
>  arch/mips/ralink/Kconfig   |   9 +-
>  3 files changed, 633 insertions(+), 1 deletion(-)
>  create mode 100644 arch/mips/pci/pci-mt7621.c
> 
> diff --git a/arch/mips/pci/Makefile b/arch/mips/pci/Makefile
> index f3eecc065e5c..178c550739c4 100644
> --- a/arch/mips/pci/Makefile
> +++ b/arch/mips/pci/Makefile
> @@ -24,6 +24,7 @@ obj-$(CONFIG_PCI_AR2315)	+= pci-ar2315.o
>  obj-$(CONFIG_SOC_AR71XX)	+= pci-ar71xx.o
>  obj-$(CONFIG_PCI_AR724X)	+= pci-ar724x.o
>  obj-$(CONFIG_PCI_XTALK_BRIDGE)	+= pci-xtalk-bridge.o
> +obj-$(CONFIG_PCI_MT7621)	+= pci-mt7621.o
>  #
>  # These are still pretty much in the old state, watch, go blind.
>  #
> diff --git a/arch/mips/pci/pci-mt7621.c b/arch/mips/pci/pci-mt7621.c
> new file mode 100644
> index 000000000000..fe1945819d25
> --- /dev/null
> +++ b/arch/mips/pci/pci-mt7621.c
...
> +static int mt7621_pcie_enable_ports(struct mt7621_pcie *pcie)
> +{
> +	struct device *dev = pcie->dev;
> +	struct mt7621_pcie_port *port;
> +	u8 num_slots_enabled = 0;
> +	u32 slot;
> +	u32 val;
> +	int err;
> +
> +	/* Setup MEMWIN and IOWIN */
> +	pcie_write(pcie, 0xffffffff, RALINK_PCI_MEMBASE);
> +	pcie_write(pcie, pcie->io.start, RALINK_PCI_IOBASE);
> +
> +	list_for_each_entry(port, &pcie->ports, list) {
> +		if (port->enabled) {
> +			err = clk_prepare_enable(port->clk);
> +			if (err) {
> +				dev_err(dev, "enabling clk pcie%d\n", slot);
> +				return err;
> +			}
> +
> +			mt7621_pcie_enable_port(port);
> +			dev_info(dev, "PCIE%d enabled\n", port->slot);
> +			num_slots_enabled++;
> +		}
> +	}
> +
> +	for (slot = 0; slot < num_slots_enabled; slot++) {
> +		val = read_config(pcie, slot, PCI_COMMAND);
> +		val |= PCI_COMMAND_MASTER;
> +		write_config(pcie, slot, PCI_COMMAND, val);

Hello! Is this part of code correct? Because it looks strange if PCIe
controller driver automatically enables PCI bus mastering, prior device
driver initialize itself.

Moreover kernel has already function pci_set_master() for this purpose
which is used by device drivers.

So I think this code can confuse some device drivers...

> +		/* configure RC FTS number to 250 when it leaves L0s */
> +		val = read_config(pcie, slot, PCIE_FTS_NUM);
> +		val &= ~PCIE_FTS_NUM_MASK;
> +		val |= PCIE_FTS_NUM_L0(0x50);
> +		write_config(pcie, slot, PCIE_FTS_NUM, val);
> +	}
> +
> +	return 0;
> +}