linux-kernel - Re: [PATCH v4 2/2] PCI: Add tango PCIe host bridge support

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Message-ID: <57673076-4fbd-92ab-453c-3d77fd65407f@free.fr>
Date:   Thu, 25 May 2017 14:00:31 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        David Laight <david.laight@...lab.com>,
        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>
Subject: Re: [PATCH v4 2/2] PCI: Add tango PCIe host bridge support

On 25/05/2017 10:48, Marc Zyngier wrote:

> On 20/04/17 15:31, Marc Gonzalez wrote:
>
>> This driver is required to work around several hardware bugs in the
>> PCIe controller.
>>
>> NB: Revision 1 does not support legacy interrupts, or IO space.
>>
>> Signed-off-by: Marc Gonzalez <marc_gonzalez@...madesigns.com>
>> ---
>>  Documentation/devicetree/bindings/pci/tango-pcie.txt |  32 ++++++++
>>  drivers/pci/host/Kconfig                             |   8 ++
>>  drivers/pci/host/Makefile                            |   1 +
>>  drivers/pci/host/pcie-tango.c                        | 161 +++++++++++++++++++++++++++++++++++++++
>>  include/linux/pci_ids.h                              |   2 +
>>  5 files changed, 204 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/pci/tango-pcie.txt b/Documentation/devicetree/bindings/pci/tango-pcie.txt
>> new file mode 100644
>> index 000000000000..3353b4e77309
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/pci/tango-pcie.txt
>> @@ -0,0 +1,32 @@
>> +Sigma Designs Tango PCIe controller
>> +
>> +Required properties:
>> +
>> +- compatible: "sigma,smp8759-pcie"
>> +- reg: address/size of PCI configuration space, address/size of register area
>> +- device_type: "pci"
>> +- #size-cells: <2>
>> +- #address-cells: <3>
>> +- #interrupt-cells: <1>
> 
> What is the point of having an #interrupt-cells when this is *not* an
> interrupt controller (as it doesn't support legacy interrupts)?

My mistake.

Thanks for kindly pointing out that the #interrupt-cells property
is not needed when a controller doesn't support legacy interrupts.

If a controller does support legacy interrupts, then I see other
bindings define #interrupt-cells and interrupt-map.
Is interrupt-controller also required?
Is that redundant with msi-controller?

(Rev2 will support legacy interrupts.)

References for my own information:
http://elixir.free-electrons.com/linux/latest/source/Documentation/devicetree/bindings/pci/host-generic-pci.txt
http://elixir.free-electrons.com/linux/latest/source/Documentation/devicetree/bindings/pci/altera-pcie.txt
http://elinux.org/Device_Tree_Usage#Advanced_Interrupt_Mapping

> As mentioned earlier, this needs to be a separate patch to be reviewed
> by the Keepers of the Faith (aka the DT maintainers).

robh already acked v3 two months ago, but can split it up,
and CC the DT folks for v5.

>> +static int smp8759_init(struct tango_pcie *pcie, void __iomem *base)
>> +{
>> +	pcie->mux		= base + 0x48;
>> +	pcie->msi_status	= base + 0x80;
>> +	pcie->msi_enable	= base + 0xa0;
>> +	pcie->msi_doorbell	= 0xa0000000 + 0x2e07c;
>> +
>> +	return tango_check_pcie_link(base + 0x74);
> 
> Please have some defines for these magic values.

Typical driver do
#define MUX_OFFSET 0x48
and then access the register's value through
readl_relaxed(pcie->base + MUX_OFFSET);

I can't do that because the registers were shuffled around
between revision 1 and revision 2. Thus, instead of an
explicitly-named macro (MUX_OFFSET), I used an explicitly-
named field (pcie->mux) and access the register's value
through readl_relaxed(pcie->mux);

This is equivalent to providing the offset definitions in the
init functions, instead of at the top of the file.

Regards.