Date:   Thu, 19 Oct 2017 19:04:56 -0400
From:   Jim Quinlan <jim2101024@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux-MIPS <linux-mips@...ux-mips.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Kevin Cernekee <cernekee@...il.com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
        Gregory Fong <gregory.0xf0@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Brian Norris <computersforpeace@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/9] PCI: host: brcmstb: add DT docs for Brcmstb PCIe device

On Thu, Oct 19, 2017 at 5:49 PM, Rob Herring <robh@...nel.org> wrote:
> On Tue, Oct 17, 2017 at 5:42 PM, Jim Quinlan <jim2101024@...il.com> wrote:
>> On Tue, Oct 17, 2017 at 4:24 PM, Rob Herring <robh@...nel.org> wrote:
>>> On Wed, Oct 11, 2017 at 06:34:22PM -0400, Jim Quinlan wrote:
>>>> The DT bindings description of the Brcmstb PCIe device is described.  This
>>>> node can be used by almost all Broadcom settop box chips, using
>>>> ARM, ARM64, or MIPS CPU architectures.
>>>>
>>>> Signed-off-by: Jim Quinlan <jim2101024@...il.com>
>>>> ---
>>>>  .../devicetree/bindings/pci/brcmstb-pci.txt        | 106 +++++++++++++++++++++
>>>>  1 file changed, 106 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/pci/brcmstb-pci.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/pci/brcmstb-pci.txt b/Documentation/devicetree/bindings/pci/brcmstb-pci.txt
>>>> new file mode 100644
>>>> index 0000000..2f699da
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/pci/brcmstb-pci.txt
>>>> @@ -0,0 +1,106 @@
>>>> +Brcmstb PCIe Host Controller Device Tree Bindings
>>>> +We don't; this line is erroneous.
>>>> +Introduction:
>>>> +  The brcmstb host controller closely follows the example set in
>>>> +
>>>> +     [1] http://devicetree.org/Device_Tree_Usage#PCI_Host_Bridge
>>>> +
>>>> +  The rest of this document explains some added customizations and
>>>> +  offers an example Brcmstb PCIe host controller DT node.
>>>> +
>>>> +Required Properties:
>>>> +  reg -- the register start address and length for the PCIe block.
>>>> +      Additional start,length pairs may be specified for clock addresses.
>>>
>>> Kind of vague and why do you need clock addresses and the clock binding?
>>>
>> We don't;  this line is erroneous and will be removed.
>>
>>> Also, typically the config space is defined here? Is that missing or you
>>> don't support memory mapped config space?
>>>
>> We do not support memory mapped config space.
>>
>>>> +  interrupts -- two interrupts are specified; the first interrupt is for
>>>> +      the PCI host controller and the second is for MSI if the built-in
>>>> +      MSI controller is to be used.
>>>> +  interrupt-names -- names of the interrupts (above): "pcie" and "msi".
>>>> +  compatible -- must be one of: "brcm,bcm7425-pcie", "brcm,bcm7435-pcie",
>>>> +      or "brcm,bcm7278-pcie".
>>>
>>> One compatible per line.
>>>
>> Will fix.
>>
>>>> +  #address-cells -- the number of address cells for PCI-space.
>>>> +  #size-cells -- the number of size cells for PCI-space.
>>>> +  ranges -- See [1]; a specification of the outbound windows for the host
>>>> +      controller.  Each outbound window is described by a n-tuple:
>>>> +          (3 cells) -- PCIe space start address; one cell for attributes
>>>> +                       and two cells for the 64-bit PCIe address.
>>>> +          (x cells) -- CPU/System start address, number of cells is determined
>>>> +                       by the parent node's #address-cells.
>>>> +          (y cells) -- Size of region, number of cells determined by the
>>>> +                       parent node's #size-cells.
>>>> +      Due to hardware limitations, there may be a maximum of four
>>>> +      non-contiguous ranges specified.We don't; this line is erroneous.
>>>> +  #interrupt-cells -- number of cells used to describe the interrupt.
>>>
>>> How many cells?
>>>
>> This line will be removed.
>
> Humm, why? You need it to have interrupt-map. You just need to say
> what the value is, not what the property is.

Okay, I got this from
https://elinux.org/Device_Tree_Usage#Advanced_Interrupt_Mapping  which
says that
"First you'll notice that PCI interrupt numbers use only one cell,
unlike the system interrupt controller which uses 2 cells; one for the
irq number, and one for flags. PCI only needs one cell for interrupts
because PCI interrupts are specified to always be level-low
sensitive."  Is that not the convention for legacy PCI interrupts?

>
>>>> +  interrupt-map-mask -- see [1]; four cells, the first three are zero
>>>> +      for our uses and the fourth cell is the mask (val = 0x7) for
>>>> +      the legacy interrupt number [1..4].
>>>> +  interrupt-map -- See [1]; there are four interrupts (INTA, INTB,
>>>> +      INTC, and INTD) to be mapped; each interrupt requires 5 cells
>>>> +      plus the size of the interrupt specifier.
>>>> +  linux,pci-domain -- the domain of the host controller.
>>>> +
>>>> +Optional Properties:
>>>> +  clocks -- list of clock phandles.  If specified, this should list one
>>>> +      clock.
>>>> +  clock-names -- the "local" names of the clocks specified in 'clocks'.  Note
>>>> +      that if the 'clocks' property is given, 'clock-names' is mandatory,
>>>> +      and the name of the clock is expected to be "sw_pcie".
>>>> +  dma-ranges -- Similar in structure to ranges, each dma region is
>>>> +      specified with a n-tuple.  Dma-regions describe the inbound
>>>> +      accesses from EP to RC; it translates the pci address that the
>>>> +      EP "sees" to the CPU address in memory.  This property is needed
>>>> +      because the design of the Brcmstb memory subsystem often precludes
>>>> +      idenity-mapping between CPU address space and PCIe address space.
>>>> +      Each range is described by a n-tuple:
>>>> +          (3 cells) -- PCIe space start address; one cell for attributes
>>>> +                       and two cells for the 64-bit PCIe address.
>>>> +          (x cells) -- CPU/System start address, number of cells is determined
>>>> +                       by the parent node's #address-cells.
>>>> +          (y cells) -- Size of region, number of cells determined by the
>>>> +                       parent node's #size-cells.
>>>
>>> There's no need to describe standard properties. Just put whatever is
>>> specific to your platform. That applies throughout this doc.
>>>
>> Will fix.
>>
>>>> +  msi-parent -- if MSI is to be used, this must be a phandle to the
>>>> +      msi-parent.  If this prop is set to the phandle of the PCIe
>>>> +      node, or if the msi-parent prop is missing, the PCIE controller
>>>> +      will attempt to use its built in MSI controller.
>>>> +  msi-controller -- this property should only be specified if the
>>>> +      PCIe controller is using its internal MSI controller.
>>>> +  brcm,ssc -- (boolean) indicates usage of spread-spectrum clocking.
>>>> +  brcm,gen --  (integer) indicates desired generation of link:
>>>> +      1 => 2.5 Gbps, 2 => 5.0 Gbps, 3 => 8.0 Gbps.
>>>
>>> We have a standard property for this IIRC.
>>>
>> Yes, BrianN pointed that out and it will be fixed.
>>
>>>> +  supply-names -- the names of voltage regulators that the root
>>>> +      complex should turn off/on/on on suspend/resume/boot.  This
>>>> +      is a string list.
>>>> +  supplies -- A collection of phandles to a regulator nodes, see
>>>> +      Documentation/devicetree/bindings/regulator/ for specificWe don't; this line is erroneous.
>>>> +      bindings. The number and order of phandles must match
>>>> +      exactly the number of strings in the "supply-names" property.
>>>
>>> This is not the regulator binding. Use the standard binding.
>>>
>> The reason we do it this way is because the PCIe controller does not
>> know or care what the names of the supplies are, or how many there
>> will be.  The list of regulators can be different for each board we
>> support, as these regulators turn on/off the downstream EP device.
>> All the PCIe controller does is turn on/off this list of regulators
>> when booting,resuming/suspending.
>>
>> An alternative would have the node specifying the standard properties
>>
>> xyz-supply = <&xyz_reg>;
>> abc-supply = <&abc_reg>;
>> pdq-supply = <&pdq_reg>;
>> ...
>>
>> and then have this driver search all of the properties in the PCIe
>> node for names matching /-supply$/, and then create a list of phandles
>> from that.  Is that what you would like?
>
> Really, you should have child nodes of the PCIe devices and have the
> supplies in there.
>
> The driver could do what you describe, but you've still got to define
> the names here.
>
> Rob

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