linux-kernel - Re: [PATCH v8 3/6] pci:host: Add Altera PCIe host controller driver

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Message-ID: <20151008094744.GD32532@n2100.arm.linux.org.uk>
Date:	Thu, 8 Oct 2015 10:47:44 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Ley Foon Tan <lftan@...era.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Marc Zyngier <marc.zyngier@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Dinh Nguyen <dinguyen@...nsource.altera.com>,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, lftan.linux@...il.com,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v8 3/6] pci:host: Add Altera PCIe host controller driver

On Thu, Oct 08, 2015 at 05:43:11PM +0800, Ley Foon Tan wrote:
> +static int altera_pcie_cfg_write(struct pci_bus *bus, unsigned int devfn,
> +				 int where, int size, u32 value)
> +{
> +	struct altera_pcie *pcie = bus->sysdata;
> +	u32 data32;
> +	u32 shift = 8 * (where & 3);
> +	int ret;
> +
> +	if (!altera_pcie_valid_config(pcie, bus, PCI_SLOT(devfn)))
> +		return PCIBIOS_DEVICE_NOT_FOUND;
> +
> +	/* write partial */
> +	if (size != sizeof(u32)) {
> +		ret = tlp_cfg_dword_read(pcie, bus->number, devfn,
> +					 where & ~DWORD_MASK, &data32);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	switch (size) {
> +	case 1:
> +		data32 = (data32 & ~(0xff << shift)) |
> +				((value & 0xff) << shift);
> +		break;
> +	case 2:
> +		data32 = (data32 & ~(0xffff << shift)) |
> +				((value & 0xffff) << shift);
> +		break;
> +	default:
> +		data32 = value;

Can you generate proper 1, 2 and 4 byte configuration accesses?  That
is much preferred over the above read-modify-write, as there are
registers in PCI and PCIe that are read/write-1-to-clear.  The above
has the effect of inadvertently clearing those RW1C bits.

-- 
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according to speedtest.net.
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