linux-kernel - Re: [PATCH v6 07/12] soc: aspeed: xdma: Add user interface

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Date:   Fri, 17 Jan 2020 10:39:33 +1030
From:   "Andrew Jeffery" <andrew@...id.au>
To:     "Eddie James" <eajames@...ux.ibm.com>,
        linux-aspeed@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        mark.rutland@....com, "Jason Cooper" <jason@...edaemon.net>,
        "Marc Zyngier" <maz@...nel.org>,
        "Rob Herring" <robh+dt@...nel.org>, tglx@...utronix.de,
        "Joel Stanley" <joel@....id.au>
Subject: Re: [PATCH v6 07/12] soc: aspeed: xdma: Add user interface



On Thu, 16 Jan 2020, at 07:59, Eddie James wrote:
> This commits adds a miscdevice to provide a user interface to the XDMA
> engine. The interface provides the write operation to start DMA
> operations. The DMA parameters are passed as the data to the write call.
> The actual data to transfer is NOT passed through write. Note that both
> directions of DMA operation are accomplished through the write command;
> BMC to host and host to BMC.
> 
> The XDMA driver reserves an area of physical memory for DMA operations,
> as the XDMA engine is restricted to accessing certain physical memory
> areas on some platforms. This memory forms a pool from which users can
> allocate pages for their usage with calls to mmap. The space allocated
> by a client will be the space used in the DMA operation. For an
> "upstream" (BMC to host) operation, the data in the client's area will
> be transferred to the host. For a "downstream" (host to BMC) operation,
> the host data will be placed in the client's memory area.
> 
> Poll is also provided in order to determine when the DMA operation is
> complete for non-blocking IO.
> 
> Signed-off-by: Eddie James <eajames@...ux.ibm.com>

Reviewed-by: Andrew Jeffery <andrew@...id.au>