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

[Robin Murphy]

On 2020-05-04 9:44 am, Kishon Vijay Abraham I wrote:
> 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@xxxxxx>
> > > > ---
> > > >  Â drivers/pci/controller/cadence/pcie-cadence-host.c | 13 +++++++++++--
> > > >  Â 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)
> > > >  ÂÂÂÂÂ struct device *dev = rc->pcie.dev;
> > > >  ÂÂÂÂÂ struct platform_device *pdev = to_platform_device(dev);
> > > >  ÂÂÂÂÂ struct device_node *np = dev->of_node;
> > > > +ÂÂÂ struct of_pci_range_parser parser;
> > > >  ÂÂÂÂÂ struct pci_host_bridge *bridge;
> > > >  ÂÂÂÂÂ struct list_head resources;
> > > > +ÂÂÂ struct of_pci_range range;
> > > >  ÂÂÂÂÂ struct cdns_pcie *pcie;
> > > >  ÂÂÂÂÂ struct resource *res;
> > > >  ÂÂÂÂÂ int ret;
> > > > @@ -222,8 +224,15 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
> > > >  ÂÂÂÂÂ rc->max_regions = 32;
> > > >  ÂÂÂÂÂ of_property_read_u32(np, "cdns,max-outbound-regions", &rc->max_regions);
> > > >  Â -ÂÂÂ rc->no_bar_nbits = 32;
> > > > -ÂÂÂ of_property_read_u32(np, "cdns,no-bar-match-nbits", &rc->no_bar_nbits);
> > > > +ÂÂÂ if (!of_pci_dma_range_parser_init(&parser, np))
> > > > +ÂÂÂÂÂÂÂ if (of_pci_range_parser_one(&parser, &range))
> > > > +ÂÂÂÂÂÂÂÂÂÂÂ 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.

OK, if anything that further strengthens the argument for deprecating a 
single "number of bits" property in favour of ranges that accurately 
describe the window(s). However it also suggests that other users in 
future might have some expectation that specifying "dma-ranges" with up 
to 3 entries should work to allow a more restrictive inbound 
configuration. Thus it would be desirable to make the code a little more 
robust here - even if we don't support multiple windows straight off, it 
would still be better to implement it in a way that can be cleanly 
extended later, and at least say something if more ranges are specified 
rather than just silently ignoring them.

> > 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.

If you give it a valid third argument it *also* parses "dma-ranges" into 
a list of inbound regions. This is already used by various other drivers 
for equivalent inbound window setup, which is what I was hinting at 
before, but given the extensibility argument above I'm now going to 
actively suggest following that pattern for consistency.

Robin.