Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: dma-coherent property for PCIe Root
To:     Valmiki <valmikibow@gmail.com>, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     lorenzo.pieralisi@arm.com, bhelgaas@google.com, robh@kernel.org
References: <1512d7b5-54c6-3b87-0090-5e370955223e@gmail.com>
From:   Jon Masters <jcm@jonmasters.org>
Organization: World Organi{s,z}ation of Broken Dreams
Message-ID: <269995f2-d57b-d218-8730-fe729cc9dec2@jonmasters.org>
Date:   Thu, 1 Oct 2020 01:16:10 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.2.2
MIME-Version: 1.0
In-Reply-To: <1512d7b5-54c6-3b87-0090-5e370955223e@gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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