Re: [PATCH v9 1/7] PCI: dwc: Use resource start as iomap() input in dw_pcie_pme_turn_off()
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2025-01-29 23:19:39
Also in:
imx, linux-devicetree, linux-pci, lkml
On Tue, Jan 28, 2025 at 05:07:34PM -0500, Frank Li wrote:
Pass resource start as the input argument to iomap() instead of atu.cpu_address in dw_pcie_pme_turn_off(). While atu.cpu_address happens to be the same here, it actually represents the parent bus address before ATU, which may not always align with the CPU address. Using resource start ensures correctness and clarity.
1) "atu.cpu_address happens to be the same here" is currently true
but only because this function is buggy and assumes the ATU input
address is the same as a CPU physical address.
2) We're trying to make a correctness fix, not a clarity fix. This
patch by itself isn't a functional change because of the cpu_addr
bug, but without this patch, fixing the cpu_addr bug would break
the iomap.
3) "Pass resource start as the input to iomap()" just restates the
patch. We should say *why* this is important. Something like
this:
The msg_res region translates writes into PCIe Message TLPs.
Previously we mapped this region using atu.cpu_addr, the input
address programmed into the ATU.
"cpu_addr" is a misnomer because when a bus fabric translates
addresses between the CPU and the ATU, the ATU input address is
different from the CPU address. A future patch will rename
"cpu_addr" and correct the value to be the ATU input address
instead of the CPU physical address.
Map the msg_res region before writing to it using the msg_res
resource start, a CPU physical address.
quoted hunk ↗ jump to hunk
Signed-off-by: Frank Li <Frank.Li@nxp.com> --- change from v9 to v10 - new patch --- drivers/pci/controller/dwc/pcie-designware-host.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c index ffaded8f2df7b..ae3fd2a5dbf85 100644 --- a/drivers/pci/controller/dwc/pcie-designware-host.c +++ b/drivers/pci/controller/dwc/pcie-designware-host.c@@ -908,7 +908,7 @@ static int dw_pcie_pme_turn_off(struct dw_pcie *pci) if (ret) return ret; - mem = ioremap(atu.cpu_addr, pci->region_align); + mem = ioremap(pci->pp.msg_res->start, pci->region_align); if (!mem) return -ENOMEM;-- 2.34.1