linux-kernel - Re: [PATCH v2 11/17] PCI: dwc: Simplify in/outbound iATU setup methods

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Date:   Thu, 12 May 2022 19:31:24 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.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>,
        Rob Herring <robh@...nel.org>,
        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>, Rob Herring <robh+dt@...nel.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 11/17] PCI: dwc: Simplify in/outbound iATU setup
 methods

On Wed, May 04, 2022 at 12:46:32AM +0300, Serge Semin wrote:
> From maintainability and scalability points of view it has been wrong to
> use different iATU inbound and outbound regions accessors for the viewport
> and unrolled versions of the iATU CSRs mapping. Seeing the particular iATU
> region-wise registers layout is almost fully compatible for different
> IP-core versions, there were no much points in splitting the code up that
> way since it was possible to implement a common windows setup methods for
> both viewport and unrolled iATU CSRs spaces. While what we can observe in
> the current driver implementation of these methods, is a lot of code
> duplication, which consequently worsen the code readability,
> maintainability and scalability. Note the current implementation is a bit
> more performant than the one suggested in this commit since it implies
> having less MMIO accesses. But the gain just doesn't worth having the
> denoted difficulties especially seeing the iATU setup methods are mainly
> called on the DW PCIe controller and peripheral devices initialization
> stage.
> 
> Here we suggest to move the iATU viewport and unrolled CSR access
> specifics in the dw_pcie_readl_atu() and dw_pcie_writel_atu() method, and
> convert the dw_pcie_prog_outbound_atu() and
> dw_pcie_prog_{ep_}inbound_atu() functions to being generic instead of
> having a different methods for each viewport and unrolled types of iATU
> CSRs mapping. Nothing complex really. First of all the dw_pcie_readl_atu()
> and dw_pcie_writel_atu() are converted to accept relative iATU CSRs
> address together with the iATU region direction (inbound or outbound) and
> region index. If DW PCIe controller doesn't have the unrolled iATU CSRs
> space, then the accessors will need to activate a iATU viewport based on
> the specified direction and index, otherwise a base address for the
> corresponding region CSRs will be calculated by means of the
> PCIE_ATU_UNROLL_BASE() macro. The CSRs macro have been modified in
> accordance with that logic in the pcie-designware.h header file.
> 
> The rest of the changes in this commit just concern converting the iATU
> in-/out-bound setup methods and iATU regions detection procedure to be
> compatible with the new accessors semantics. As a result we've dropped the
> no more required dw_pcie_prog_outbound_atu_unroll(),
> dw_pcie_prog_inbound_atu_unroll() and dw_pcie_iatu_detect_regions_unroll()
> methods.
> 
> Note aside with the denoted code improvements, there is an additional
> positive side effect of this change. If at some point an atomic iATU
> configs setup procedure is required, it will be possible to be done with
> no much effort just by adding the synchronization into the
> dw_pcie_readl_atu() and dw_pcie_writel_atu() accessors.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> ---
> 
> Changelog v2:
> - Move the iATU region selection procedure into a helper function (@Rob).
> - Simplify the iATU region selection procedure by recalculating the base
>   address only if the space is unrolled. The iATU viewport base address
>   is saved in the pci->atu_base field from now.
> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 293 ++++++-------------
>  drivers/pci/controller/dwc/pcie-designware.h |  48 ++-

In this patch, you also need to fix "pcie-tegra194-acpi.c" driver that makes
use of the removed macros.

Thanks,
Mani

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