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charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 5/22/2019 7:32 PM, Bjorn Helgaas wrote: > On Wed, May 22, 2019 at 02:26:08PM +0530, Vidya Sagar wrote: >> On 5/22/2019 2:47 AM, Bjorn Helgaas wrote: >>> On Fri, May 17, 2019 at 06:08:35PM +0530, Vidya Sagar wrote: >>>> Move PCIe config space capability search API to common DesignWare file >>>> as this can be used by both host and ep mode codes. > >>>> .../pci/controller/dwc/pcie-designware-ep.c | 37 +---------------- >>>> drivers/pci/controller/dwc/pcie-designware.c | 40 +++++++++++++++++++ >>>> drivers/pci/controller/dwc/pcie-designware.h | 2 + >>>> 3 files changed, 44 insertions(+), 35 deletions(-) > >>>> --- a/drivers/pci/controller/dwc/pcie-designware.c >>>> +++ b/drivers/pci/controller/dwc/pcie-designware.c >>>> @@ -14,6 +14,46 @@ >>>> #include "pcie-designware.h" >>>> +/* >>>> + * These APIs are different from standard pci_find_*capability() APIs in the >>>> + * sense that former can only be used post device enumeration as they require >>>> + * 'struct pci_dev *' pointer whereas these APIs require 'struct dw_pcie *' >>>> + * pointer and can be used before link up also. >>> >>> I think this comment is slightly misleading because it suggests the >>> reason we need these DW interfaces is because we're doing something >>> before a pci_dev pointer is available. >>> >>> But these DW interfaces are used on devices that will *never* have a >>> pci_dev pointer because they are not PCI devices. They're used on >>> host controller devices, which have a PCIe link on the downstream >>> side, but the host controller driver operates them using their >>> upstream, non-PCI interfaces. Logically, I think they would be >>> considered parts of Root Complexes, not Root Ports. >>> >>> There's actually no reason why that upstream interface should look >>> anything like PCI; it doesn't need to organize registers into >>> capability lists at all. It might be convenient for the hardware to >>> do that and share things with a Root Port device, which *is* a PCI >>> device, but it's not required. >>> >>> It also really has nothing to do with whether the link is up. This >>> code operates on hardware that is upstream from the link, so we can >>> reach it regardless of the link. >> >> I added this comment after receiving a review comment to justify why >> standard pci_find_*capability() APIs can't be used here. Hence added >> this. I understand your comment that DW interface need not have to >> be a PCI device, but what is present in the hardware is effectively >> a root port implementation and post enumeration, we get a 'struct >> pci_dev' created for it, hence I thought it is fine to bring 'struct >> pci_dev' into picture. > > This code operates on the host controller. It configures the bridge > that leads *to* PCI devices. Since that bridge is not a PCI device, > the PCI specs don't say anything about how to program it. > > The fact that the host controller programming interface happens to > resemble the PCI programming interface is purely coincidental. > >> Also, I agree that mention of 'link up' is unwarranted and could be >> reworded in a better way. >> >> Do you suggest to remove this comment altogether or reword it s/and >> can be used before link up also/and can be used before 'struct >> pci_dev' is available/ ? > > Maybe something like this? > > These interfaces resemble the pci_find_*capability() interfaces, > but these are for configuring host controllers, which are bridges > *to* PCI devices but are not PCI devices themselves. Ok. Done. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel