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Subject: Re: [PATCH 1/3] dt-bindings: PCI: cadence: Deprecate inbound/outbound
 specific bindings
From:   Kishon Vijay Abraham I <kishon@ti.com>
To:     Rob Herring <robh@kernel.org>
CC:     Tom Joseph <tjoseph@cadence.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Andrew Murray <amurray@thegoodpenguin.co.uk>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        <linux-pci@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20200327104727.4708-1-kishon@ti.com>
 <20200327104727.4708-2-kishon@ti.com> <20200330160142.GA6259@bogus>
 <2a18a228-9248-24a8-c9cd-a041c62aa381@ti.com> <20200331164529.GA32149@bogus>
 <2985575e-e079-2a8d-bf3e-b7efb7291fc3@ti.com>
Message-ID: <f335a8be-d292-8e74-0657-d37e7ae55fdc@ti.com>
Date:   Fri, 3 Apr 2020 11:12:13 +0530
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Hi Rob,

On 4/1/2020 8:38 AM, Kishon Vijay Abraham I wrote:
> Hi Rob,
> 
> On 3/31/2020 10:15 PM, Rob Herring wrote:
>> On Tue, Mar 31, 2020 at 09:08:12AM +0530, Kishon Vijay Abraham I wrote:
>>> Hi Rob,
>>>
>>> On 3/30/2020 9:31 PM, Rob Herring wrote:
>>>> On Fri, Mar 27, 2020 at 04:17:25PM +0530, Kishon Vijay Abraham I wrote:
>>>>> Deprecate cdns,max-outbound-regions and cdns,no-bar-match-nbits for
>>>>> host mode as both these could be derived from "ranges" and "dma-ranges"
>>>>> property. "cdns,max-outbound-regions" property would still be required
>>>>> for EP mode.
>>>>>
>>>>> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
>>>>> ---
>>>>>  .../bindings/pci/cdns,cdns-pcie-ep.yaml       |  2 +-
>>>>>  .../bindings/pci/cdns,cdns-pcie-host.yaml     |  3 +--
>>>>>  .../devicetree/bindings/pci/cdns-pcie-ep.yaml | 25 +++++++++++++++++++
>>>>>  .../bindings/pci/cdns-pcie-host.yaml          | 10 ++++++++
>>>>>  .../devicetree/bindings/pci/cdns-pcie.yaml    |  8 ------
>>>>>  5 files changed, 37 insertions(+), 11 deletions(-)
>>>>>  create mode 100644 Documentation/devicetree/bindings/pci/cdns-pcie-ep.yaml
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-ep.yaml b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-ep.yaml
>>>>> index 2996f8d4777c..50ce5d79d2c7 100644
>>>>> --- a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-ep.yaml
>>>>> +++ b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-ep.yaml
>>>>> @@ -10,7 +10,7 @@ maintainers:
>>>>>    - Tom Joseph <tjoseph@cadence.com>
>>>>>  
>>>>>  allOf:
>>>>> -  - $ref: "cdns-pcie.yaml#"
>>>>> +  - $ref: "cdns-pcie-ep.yaml#"
>>>>>    - $ref: "pci-ep.yaml#"
>>>>>  
>>>>>  properties:
>>>>> diff --git a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
>>>>> index cabbe46ff578..84a8f095d031 100644
>>>>> --- a/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
>>>>> +++ b/Documentation/devicetree/bindings/pci/cdns,cdns-pcie-host.yaml
>>>>> @@ -45,8 +45,6 @@ examples:
>>>>>              #size-cells = <2>;
>>>>>              bus-range = <0x0 0xff>;
>>>>>              linux,pci-domain = <0>;
>>>>> -            cdns,max-outbound-regions = <16>;
>>>>> -            cdns,no-bar-match-nbits = <32>;
>>>>>              vendor-id = <0x17cd>;
>>>>>              device-id = <0x0200>;
>>>>>  
>>>>> @@ -57,6 +55,7 @@ examples:
>>>>>  
>>>>>              ranges = <0x02000000 0x0 0x42000000  0x0 0x42000000  0x0 0x1000000>,
>>>>>                       <0x01000000 0x0 0x43000000  0x0 0x43000000  0x0 0x0010000>;
>>>>> +            dma-ranges = <0x02000000 0x0 0x0 0x0 0x0 0x1 0x00000000>;
>>>>>  
>>>>>              #interrupt-cells = <0x1>;
>>>>>  
>>>>> diff --git a/Documentation/devicetree/bindings/pci/cdns-pcie-ep.yaml b/Documentation/devicetree/bindings/pci/cdns-pcie-ep.yaml
>>>>> new file mode 100644
>>>>> index 000000000000..6150a7a7bdbf
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/pci/cdns-pcie-ep.yaml
>>>>> @@ -0,0 +1,25 @@
>>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>>> +%YAML 1.2
>>>>> +---
>>>>> +$id: "http://devicetree.org/schemas/pci/cdns-pcie-ep.yaml#"
>>>>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>>>>> +
>>>>> +title: Cadence PCIe Device
>>>>> +
>>>>> +maintainers:
>>>>> +  - Tom Joseph <tjoseph@cadence.com>
>>>>> +
>>>>> +allOf:
>>>>> +  - $ref: "cdns-pcie.yaml#"
>>>>> +
>>>>> +properties:
>>>>> +  cdns,max-outbound-regions:
>>>>> +    description: maximum number of outbound regions
>>>>> +    allOf:
>>>>> +      - $ref: /schemas/types.yaml#/definitions/uint32
>>>>> +    minimum: 1
>>>>> +    maximum: 32
>>>>> +    default: 32
>>>>
>>>> I have a feeling that as the PCI endpoint binding evolves this won't be 
>>>> necessary. I can see a common need to define the number of BARs for an 
>>>> endpoint and then this will again just be error checking.
>>>
>>> For every buffer given by the host, we have to create a new outbound
>>> translation. If there are no outbound regions, we have to report the error to
>>> the endpoint function driver. At-least for reporting the error, we'd need to
>>> have this binding no?
>>
>> But isn't the endpoint defined to have some number of BARs? The PCI host 
>> doesn't decide that.
> 
> cdns,max-outbound-regions defined here doesn't configure the BARs. BARs provide
> an interface for the host to access the endpoints memory. IOW for BARs we
> configure the inbound address translation unit.
> 
> cdns,max-outbound-regions is used while configuring the outbound address
> translation unit. Outbound regions are used while the endpoint access host
> memory and in that path endpoint BARs doesn't come.
>>
>>>>
>>>> What's the result if you write to a non-existent region in register 
>>>> CDNS_PCIE_AT_OB_REGION_PCI_ADDR0/1? If the register is non-existent and 
>>>> doesn't abort, you could detect this instead.
>>>
>>> I'm not sure if we should ever try to write to a non-existent register though
>>> the behavior could be different in different platforms. IMHO maximum number of
>>> outbound regions is a HW property and is best described in device tree.
>>
>> AIUI, PCI defines non-existent (config space) registers to return all 
>> 1s. Not sure if this register is in PCI config space or the host SoC bus 
>> (e.g. AXI). It seems PCI bridges get done both ways from what I've seen.
> 
> All of that is correct for the Host or RC. However here
> cdns,max-outbound-regions is an endpoint specific property (defined only in
> cdns-pcie-ep.yaml) and is useful while configuring OB address translation unit
> for the endpoint to access host memory.

Do you still have concerns regarding this? If you don't have any further
comments on this, can you give your Acked-by please?

Thanks
Kishon