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SubjectRe: [PATCH v5 3/6] PCI: brcmstb: Add Broadcom STB PCIe host controller driver
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On Wed, 2020-01-15 at 10:00 +0000, Lorenzo Pieralisi wrote:
> On Tue, Jan 14, 2020 at 07:18:46PM +0100, Nicolas Saenz Julienne wrote:
> > Hi Lorenzo,
> >
> > On Tue, 2020-01-14 at 17:11 +0000, Lorenzo Pieralisi wrote:
> > > On Mon, Dec 16, 2019 at 12:01:09PM +0100, Nicolas Saenz Julienne wrote:
> > > > From: Jim Quinlan <james.quinlan@broadcom.com>
> > > >
> > > > This adds a basic driver for Broadcom's STB PCIe controller, for now
> > > > aimed at Raspberry Pi 4's SoC, bcm2711.
> > > >
> > > > Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
> > > > Co-developed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> > > > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> > > > Reviewed-by: Andrew Murray <andrew.murray@arm.com>
> > > > Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>
> > > >
> > > > ---
> > > >
> > > > Changes since v3:
> > > > - Update commit message
> > > > - rollback roundup_pow_two usage, it'll be updated later down the line
> > > > - Remove comment in register definition
> > > >
> > > > Changes since v2:
> > > > - Correct rc_bar2_offset sign
> > >
> > > In relation to this change.
> > >
> > > [...]
> > >
> > > > +static inline int brcm_pcie_get_rc_bar2_size_and_offset(struct
> > > > brcm_pcie
> > > > *pcie,
> > > > + u64
> > > > *rc_bar2_size,
> > > > + u64
> > > > *rc_bar2_offset)
> > > > +{
> > > > + struct pci_host_bridge *bridge =
> > > > pci_host_bridge_from_priv(pcie);
> > > > + struct device *dev = pcie->dev;
> > > > + struct resource_entry *entry;
> > > > +
> > > > + entry = resource_list_first_type(&bridge->dma_ranges,
> > > > IORESOURCE_MEM);
> > > > + if (!entry)
> > > > + return -ENODEV;
> > > > +
> > > > + *rc_bar2_offset = -entry->offset;
> > >
> > > I think this deserves a comment - I guess it has to do with how the
> > > controller expects CPU<->PCI offsets to be expressed compared to how it
> > > is computed in dma_ranges entries.
> >
> > You're right, OF code calculates it by doing:
> >
> > offset = cpu_start_addr - pci_start_addr (see
> > devm_of_pci_get_host_bridge_resources())
> >
> > While the RC_BAR2_CONFIG register expects the opposite subtraction.
> > I'll add a comment on the next revision.
>
> There is no need for a new posting, either write that comment here
> and I update the code or inline the patch or just resend *this* updated
> patch to the list.

OK, hope this sounds good enough:

/*
* The controller expects the inbound window offset to be calculated as
* the difference between PCIe's address space and CPU's. The offset
* provided by the firmware is calculated the opposite way, so we
* negate it.
*/

Regards,
Nicolas

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