linux-kernel - Re: dma-coherent property for PCIe Root

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Message-ID: <269995f2-d57b-d218-8730-fe729cc9dec2@jonmasters.org>
Date:   Thu, 1 Oct 2020 01:16:10 -0400
From:   Jon Masters <jcm@...masters.org>
To:     Valmiki <valmikibow@...il.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     lorenzo.pieralisi@....com, bhelgaas@...gle.com, robh@...nel.org
Subject: Re: dma-coherent property for PCIe Root

On 9/14/20 1:23 AM, Valmiki wrote:
> Hi All,
> 
> How does "dma-coherent" property will work for PCIe as RC on an
> ARM SOC ?
> Because the end point device drivers are the one which will request dma 
> buffers and Root port driver doesn't involve in data path of end point
> except for handling interrupts.
> 
> How does EP DMA buffers will be hardware coherent if RC driver exposes
> dma-coherent property ?

This simply means that the RC supports maintaining coherency, it doesn't 
mean that the RC driver does anything. It's a property of the hardware.

Jon.

-- 
Computer Architect