linux-kernel - Re: [PATCH v4 01/17] PCI: dwc: Use the DMA-API to get the MSI address

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Date:   Tue, 7 Nov 2017 18:56:14 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Niklas Cassel <niklas.cassel@...s.com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Niklas Cassel <niklass@...s.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 01/17] PCI: dwc: Use the DMA-API to get the MSI address

On Fri, Nov 03, 2017 at 02:47:05PM +0100, Niklas Cassel wrote:
> Use the DMA-API to get the MSI address. This address will be written to
> our PCI config space and to the register which determines which AXI
> address the DWC IP will spoof for incoming MSI irqs.
> 
> Since it is a PCIe endpoint device, rather than the CPU, that is supposed
> to write to the MSI address, the proper way to get the MSI address is by
> using the DMA API, not by using virt_to_phys().
> 
> Using virt_to_phys() might work on some systems, but using the DMA API
> should work on all systems.
> 
> This is essentially the same thing as allocating a buffer in a driver
> to which the endpoint will write to. To do this, we use the DMA API.
> 
> Signed-off-by: Niklas Cassel <niklas.cassel@...s.com>

I'm expecting Jingoo and/or Joao to chime in and ack the
DesignWare-related patches.  I think all the others are in
pretty good shape.

> ---
>  drivers/pci/dwc/pcie-designware-host.c | 15 ++++++++++++---
>  drivers/pci/dwc/pcie-designware.h      |  3 ++-
>  2 files changed, 14 insertions(+), 4 deletions(-)
> ...