linux-kernel - Re: [PATCH v2 15/17] PCI: dwc: Introduce dma-ranges property support for RC-host

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Date:   Mon, 16 May 2022 16:42:20 -0500
From:   Rob Herring <robh@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 15/17] PCI: dwc: Introduce dma-ranges property support
 for RC-host

On Wed, May 04, 2022 at 12:46:36AM +0300, Serge Semin wrote:
> In accordance with the generic PCIe Root Port DT-bindings the "dma-ranges"
> property has the same format as the "ranges" property. The only difference
> is in their semantics. The "dma-ranges" property describes the PCIe-to-CPU
> memory mapping in opposite to the CPU-to-PCIe mapping of the "ranges"
> property. Even though the DW PCIe controllers are normally equipped with
> internal Address Translation Unit which inbound and outbound tables can be
> used to implement both properties semantics, it was surprise for me to
> discover that the host-related part of the DW PCIe driver currently
> supports the "ranges" property only while the "dma-ranges" windows are
> just ignored. Having the "dma-ranges" supported in the driver would be
> very handy for the platforms, that don't tolerate the 1:1 CPU-PCIe memory
> mapping and require customized the PCIe memory layout. So let's fix that
> by introducing the "dma-ranges" property support.
> 
> First of all we suggest to rename the dw_pcie_prog_inbound_atu() method to
> dw_pcie_prog_ep_inbound_atu() and create a new version of the
> dw_pcie_prog_inbound_atu() function. Thus we'll have two methods for RC
> and EP controllers respectively in the same way as it has been developed
> for the outbound ATU setup methods.
> 
> Secondly aside with the memory window index and type the new
> dw_pcie_prog_inbound_atu() function will accept CPU address, PCIe address
> and size as its arguments. These parameters define the PCIe and CPU memory
> ranges which will be used to setup the respective inbound ATU mapping. The
> passed parameters need to be verified against the ATU ranges constraints
> in the same way as it is done for the outbound ranges.
> 
> Finally the DMA-ranges detected for the PCIe controller need to be
> converted into the inbound ATU entries during the host controller
> initialization procedure. It will be done in the framework of the
> dw_pcie_iatu_setup() method. Note before setting the inbound ranges up we
> need to disable all the inbound ATU entries in order to prevent unexpected
> PCIe TLPs translations defined by some third party software like
> bootloader.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> ---
>  .../pci/controller/dwc/pcie-designware-ep.c   |  4 +-
>  .../pci/controller/dwc/pcie-designware-host.c | 32 ++++++++++-
>  drivers/pci/controller/dwc/pcie-designware.c  | 57 ++++++++++++++++++-
>  drivers/pci/controller/dwc/pcie-designware.h  |  6 +-
>  4 files changed, 90 insertions(+), 9 deletions(-)

Reviewed-by: Rob Herring <robh@...nel.org>