linux-kernel - Re: [PATCH v9 4/4] PCI: dwc: Support ECAM mechanism by enabling iATU 'CFG Shift Feature'

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Message-ID: <74ccc612-beee-42a3-9ce3-947e59988f90@oracle.com>
Date: Mon, 15 Sep 2025 20:44:10 +0530
From: ALOK TIWARI <alok.a.tiwari@...cle.com>
To: Manivannan Sadhasivam <mani@...nel.org>,
        Jingoo Han
 <jingoohan1@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kwilczynski@...nel.org>,
        Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Alim Akhtar
 <alim.akhtar@...sung.com>,
        Jonathan Chocron <jonnyc@...zon.com>
Cc: linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Subject: Re: [PATCH v9 4/4] PCI: dwc: Support ECAM mechanism by enabling iATU
 'CFG Shift Feature'



On 9/9/2025 12:37 PM, Manivannan Sadhasivam wrote:
> Currently, the driver is not making use of this CFG shift feature, thereby
> creating the iATU outbound map for each config access to the devices,
> causing latency and wasting CPU cycles.
> 
> So to avoid this, configure the controller to enable CFG shift feature by
> enabling the 'CFG Shift' bit of the 'iATU Control 2 Register'.
> 
> As a result of enabling CFG shift (ECAM), there is longer a need to map the
> DBI register space separately as the DBI region falls under the 'config'
> space used for ECAM (as DBI is used to access the Root Port).

nit : there is no longer a need

Thanks,
Alok