linux-kernel - Re: [PATCH v3 2/2] PCI: Add tango PCIe host bridge support

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Message-ID: <96da696c-141a-3e8d-1fb7-2c024a295f58@free.fr>
Date:   Wed, 29 Mar 2017 14:53:47 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        David Laight <david.laight@...lab.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Phuong Nguyen <phuong_nguyen@...madesigns.com>,
        LKML <linux-kernel@...r.kernel.org>,
        DT <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] PCI: Add tango PCIe host bridge support

On 29/03/2017 14:19, Robin Murphy wrote:

> On 29/03/17 12:34, Marc Gonzalez wrote:
> 
>> +	/*
>> +	 * QUIRK #3
>> +	 * Unfortunately, config and mem spaces are muxed.
>> +	 * Linux does not support such a setting, since drivers are free
>> +	 * to access mem space directly, at any time.
>> +	 * Therefore, we can only PRAY that config and mem space accesses
>> +	 * NEVER occur concurrently.
>> +	 */
> 
> What about David's suggestion of using an IPI for safe mutual exclusion?

I was left with the impression that this wouldn't solve the problem.
If a mem space access is "in flight" on core0 when core1 starts a
config space access, an IPI will not prevent breakage.

Did I misunderstand?

For my education, what is the API to send an IPI?
And the API to handle an IPI?

>> +	if (of_device_is_compatible(dev->of_node, "sigma,smp8759-pcie"))
>> +		smp8759_init(pcie, base);
> 
> ...then retrieve it with of_device_get_match_data() here. No need to
> reinvent the wheel (or have to worry about the ordering of multiple
> compatibles once rev. n+1 comes around).

I actually asked about this on IRC. The consensus was "use what
best fits your use case". I need to do some processing based on
the revision, so I thought

  if (chip_x)
	do_chip_x_init()

was a good way to express my intent. Did I misunderstand?

For example, the init function for rev2 currently looks like this:

static void rev2_init(struct tango_pcie *pcie, void __iomem *base)
{
	void __iomem *misc_irq	= base + 0x40;
	void __iomem *doorbell	= base + 0x8c;

	pcie->mux		= base + 0x2c;
	pcie->msi_status	= base + 0x4c;
	pcie->msi_mask		= base + 0x6c;
	pcie->msi_doorbell	= 0x80000000;

	writel(lower_32_bits(pcie->msi_doorbell), doorbell + 0);
	writel(upper_32_bits(pcie->msi_doorbell), doorbell + 4);

	/* Enable legacy PCI interrupts */
	writel(BIT(15), misc_irq);
	writel(0xf << 4, misc_irq + 4);
}

>> +#define VENDOR_SIGMA	0x1105
> 
> Should this not be in include/linux/pci_ids.h?

Doh! Very likely. Thanks.

Regards.