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From: Rob Herring <robh@kernel.org>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: "Jingoo Han" <jingoohan1@gmail.com>,
	"Gustavo Pimentel" <gustavo.pimentel@synopsys.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Serge Semin" <fancer.lancer@gmail.com>,
	"Manivannan Sadhasivam" <manivannan.sadhasivam@linaro.org>,
	"Alexey Malahov" <Alexey.Malahov@baikalelectronics.ru>,
	"Pavel Parkhomenko" <Pavel.Parkhomenko@baikalelectronics.ru>,
	"Frank Li" <Frank.Li@nxp.com>,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 02/13] PCI: dwc: Don't use generic IO-ops for DBI-space access
Date: Thu, 26 May 2022 16:29:30 -0500	[thread overview]
Message-ID: <20220526212930.GN54904-robh@kernel.org> (raw)
In-Reply-To: <20220517125058.18488-3-Sergey.Semin@baikalelectronics.ru>

On Tue, May 17, 2022 at 03:50:47PM +0300, Serge Semin wrote:
> Commit c2b0c098fbd1 ("PCI: dwc: Use generic config accessors") replaced
> the locally defined DW PCIe host controller config-space accessors with
> the generic methods pci_generic_config_read() and
> pci_generic_config_write(). It was intended that the corresponding
> bus-mapping callback returned a correct virtual address of the passed PCI
> config-space register. The problem of the proposed solution was that it
> didn't take into account the way the host config-space is accessed on the
> DW PCIe. Depending on the DW PCIe IP-core synthesize parameters different
> interfaces can be used to access the host and peripheral config/memory
> spaces. The former one can be accessed via the DBI interface, while the
> later ones is reached via the AHB/AXI application bus. In case if the DW
> PCIe controller is configured to have a dedicated DBI interface, the way
> it is mapped into the IO-memory turns to be platform-specific. For such
> setups the DWC PCIe driver provides a set of the callbacks
> dw_pcie_ops.{read_dbi,write_dbi} so the platforms glue-drivers would be
> able to take into account the DBI bus IO peculiarities. Since
> commit c2b0c098fbd1 ("PCI: dwc: Use generic config accessors") these
> methods haven't been utilized during the generic host initialization
> performed by the PCIe subsystem code.
> 
> I don't really know how come there have been no problems spotted for the
> Histb/Exynos/Kirin PCIe controllers so far, but in our case with dword

Because they implement their own pci_ops for the root bus. You should 
too.

Who is 'our case'? 

> aligned IO requirement the generic config-space accessors can't be
> utilized for the host config-space. Thus in order to make sure the host
> config-space is properly accessed via the DBI bus let's get back the
> dw_pcie_rd_own_conf() and dw_pcie_wr_own_conf() methods. They are going to
> be just wrappers around the already defined
> dw_pcie_read_dbi()/dw_pcie_write_dbi() functions with proper arguments
> conversion. These methods perform the platform-specific config-space IO if
> the DBI accessors are specified, otherwise they call normal MMIO
> operations.

The idea was for DWC to not define its own way to have different 
read/write for root bus vs. child bus as many PCI host bridges need the 
same thing. So the host bridge struct now has 2 pci_ops pointers. And 
the mess of function pointer indirection is gone.

Rob

  reply	other threads:[~2022-05-26 21:29 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-17 12:50 [PATCH v3 00/13] PCI: dwc: Various fixes and cleanups Serge Semin
2022-05-17 12:50 ` [PATCH v3 01/13] PCI: dwc: Stop link in the host init error and de-initialization Serge Semin
2022-05-26 21:30   ` Rob Herring
2022-05-17 12:50 ` [PATCH v3 02/13] PCI: dwc: Don't use generic IO-ops for DBI-space access Serge Semin
2022-05-26 21:29   ` Rob Herring [this message]
2022-05-27 16:05     ` Serge Semin
2022-05-27 17:39       ` Serge Semin
2022-05-31 16:09         ` Rob Herring
2022-05-31 18:46           ` Serge Semin
2022-05-17 12:50 ` [PATCH v3 03/13] PCI: dwc: Add unroll iATU space support to the regions disable method Serge Semin
2022-05-17 12:50 ` [PATCH v3 04/13] PCI: dwc: Disable outbound windows for controllers with iATU Serge Semin
2022-05-17 12:50 ` [PATCH v3 05/13] PCI: dwc: Set INCREASE_REGION_SIZE flag based on limit address Serge Semin
2022-05-17 12:50 ` [PATCH v3 06/13] PCI: dwc: Add braces to the multi-line if-else statements Serge Semin
2022-05-17 12:50 ` [PATCH v3 07/13] PCI: dwc: Add trailing new-line literals to the log messages Serge Semin
2022-05-17 12:50 ` [PATCH v3 08/13] PCI: dwc: Discard IP-core version checking on unrolled iATU detection Serge Semin
2022-05-17 12:50 ` [PATCH v3 09/13] PCI: dwc: Convert Link-up status method to using dw_pcie_readl_dbi() Serge Semin
2022-05-17 12:50 ` [PATCH v3 10/13] PCI: dwc: Deallocate EPC memory on EP init error Serge Semin
2022-05-17 12:50 ` [PATCH v3 11/13] PCI: dwc-plat: Simplify the probe method return value handling Serge Semin
2022-05-17 12:50 ` [PATCH v3 12/13] PCI: dwc-plat: Discard unused regmap pointer Serge Semin
2022-05-17 12:50 ` [PATCH v3 13/13] PCI: dwc-plat: Drop dw_plat_pcie_of_match forward declaration Serge Semin

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