Re: [PATCH V2 0/7] Add power domain and MSI functionality with PCIe host generic ECAM driver

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Wed, Jul 24, 2024 at 10:12:17AM +0300, Dmitry Baryshkov wrote:
> On Wed, 24 Jul 2024 at 06:58, Mayank Rana <quic_mrana@quicinc.com> wrote:
> >
> >
> >
> > On 7/23/2024 7:13 PM, Dmitry Baryshkov wrote:
> > > On Mon, Jul 15, 2024 at 11:13:28AM GMT, Mayank Rana wrote:
> > >> Based on previously received feedback, this patch series adds functionalities
> > >> with existing PCIe host generic ECAM driver (pci-host-generic.c) to get PCIe
> > >> host root complex functionality on Qualcomm SA8775P auto platform.
> > >>
> > >> Previously sent RFC patchset to have separate Qualcomm PCIe ECAM platform driver:
> > >> https://lore.kernel.org/all/d10199df-5fb3-407b-b404-a0a4d067341f@quicinc.com/T/
> > >>
> > >> 1. Interface to allow requesting firmware to manage system resources and performing
> > >> PCIe Link up (devicetree binding in terms of power domain and runtime PM APIs is used in driver)
> > >> 2. Performing D3 cold with system suspend and D0 with system resume (usage of GenPD
> > >> framework based power domain controls these operations)
> > >> 3. SA8775P is using Synopsys Designware PCIe controller which supports MSI controller.
> > >> This MSI functionality is used with PCIe host generic driver after splitting existing MSI
> > >> functionality from pcie-designware-host.c file into pcie-designware-msi.c file.
> > >
> > > Please excuse me my ignorance if this is described somewhere. Why are
> > > you using DWC-specific MSI handling instead of using GIC ITS?
> > Due to usage of GIC v3 on SA8775p with Gunyah hypervisor, we have
> > limitation of not supporting GIC ITS
> > functionality. We considered other approach as usage of free SPIs (not
> > available, limitation in terms of mismatch between number of SPIs
> > available with physical GIC vs hypervisor) and extended SPIs (not
> > supported with GIC hardware). Hence we just left with DWC-specific MSI
> > controller here for MSI functionality.
> 
> ... or extend Gunyah to support GIC ITS. I'd say it is a significant
> deficiency if one can not use GIC ITS on Gunyah platforms.
> 

It if were possible, Qcom would've went with that. Unfortunately, it is not.

- Mani

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