linux-kernel - Re: [PATCH v2 2/4] PCI: cadence: Use "dma-ranges" instead of "cdns,no-bar-match-nbits" property

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Date:   Mon, 4 May 2020 14:14:29 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Robin Murphy <robin.murphy@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC:     Tom Joseph <tjoseph@...ence.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] PCI: cadence: Use "dma-ranges" instead of
 "cdns,no-bar-match-nbits" property

Hi Robin,

On 5/1/2020 9:24 PM, Robin Murphy wrote:
> On 2020-05-01 3:46 pm, Lorenzo Pieralisi wrote:
>> [+Robin - to check on dma-ranges intepretation]
>>
>> I would need RobH and Robin to review this.
>>
>> Also, An ACK from Tom is required - for the whole series.
>>
>> On Fri, Apr 17, 2020 at 05:13:20PM +0530, Kishon Vijay Abraham I wrote:
>>> Cadence PCIe core driver (host mode) uses "cdns,no-bar-match-nbits"
>>> property to configure the number of bits passed through from PCIe
>>> address to internal address in Inbound Address Translation register.
>>>
>>> However standard PCI dt-binding already defines "dma-ranges" to
>>> describe the address range accessible by PCIe controller. Parse
>>> "dma-ranges" property to configure the number of bits passed
>>> through from PCIe address to internal address in Inbound Address
>>> Translation register.
>>>
>>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>>> ---
>>>   drivers/pci/controller/cadence/pcie-cadence-host.c | 13 +++++++++++--
>>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c
>>> b/drivers/pci/controller/cadence/pcie-cadence-host.c
>>> index 9b1c3966414b..60f912a657b9 100644
>>> --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
>>> +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
>>> @@ -206,8 +206,10 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
>>>       struct device *dev = rc->pcie.dev;
>>>       struct platform_device *pdev = to_platform_device(dev);
>>>       struct device_node *np = dev->of_node;
>>> +    struct of_pci_range_parser parser;
>>>       struct pci_host_bridge *bridge;
>>>       struct list_head resources;
>>> +    struct of_pci_range range;
>>>       struct cdns_pcie *pcie;
>>>       struct resource *res;
>>>       int ret;
>>> @@ -222,8 +224,15 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
>>>       rc->max_regions = 32;
>>>       of_property_read_u32(np, "cdns,max-outbound-regions", &rc->max_regions);
>>>   -    rc->no_bar_nbits = 32;
>>> -    of_property_read_u32(np, "cdns,no-bar-match-nbits", &rc->no_bar_nbits);
>>> +    if (!of_pci_dma_range_parser_init(&parser, np))
>>> +        if (of_pci_range_parser_one(&parser, &range))
>>> +            rc->no_bar_nbits = ilog2(range.size);
> 
> You probably want "range.pci_addr + range.size" here just in case the bottom of
> the window is ever non-zero. Is there definitely only ever a single inbound
> window to consider?

Cadence IP has 3 inbound address translation registers, however we use only 1
inbound address translation register to map the entire 32 bit or 64 bit address
region.
> 
> I believe that pci_parse_request_of_pci_ranges() could do the actual parsing
> for you, but I suppose plumbing that in plus processing the resulting
> dma_ranges resource probably ends up a bit messier than the concise open-coding
> here.

right, pci_parse_request_of_pci_ranges() parses "ranges" property and is used
for outbound configuration, whereas here we parse "dma-ranges" property and is
used for inbound configuration.

Thanks
Kishon

> 
> Robin.
> 
>>> +
>>> +    if (!rc->no_bar_nbits) {
>>> +        rc->no_bar_nbits = 32;
>>> +        of_property_read_u32(np, "cdns,no-bar-match-nbits",
>>> +                     &rc->no_bar_nbits);
>>> +    }
>>>         rc->vendor_id = 0xffff;
>>>       of_property_read_u16(np, "vendor-id", &rc->vendor_id);
>>> -- 
>>> 2.17.1
>>>