linux-kernel - Re: [PATCH 6/6] serial: add amba-pl011-pci

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Message-ID: <20120526084819.GF24149@n2100.arm.linux.org.uk>
Date:	Sat, 26 May 2012 09:48:19 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alessandro Rubini <rubini@...dd.com>
Cc:	linux-kernel@...r.kernel.org,
	Giancarlo Asnaghi <giancarlo.asnaghi@...com>,
	Alan Cox <alan@...ux.intel.com>, x86@...nel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 6/6] serial: add amba-pl011-pci

One other point.

On Fri, May 25, 2012 at 05:48:57PM +0200, Alessandro Rubini wrote:
> +/* This is a template, copied every time a new pci device appears */
> +static AMBA_APB_DEVICE(pl011_pci_template, "pl011-pci", 0,
> +		       0 /* base */, {0} /* irqs */, NULL /* data */);

APB device.  It's a _peripheral_, it only has a _slave_ port which can't
initiate DMA, so:

> +	if (pdev->vendor == PCI_VENDOR_ID_STMICRO) {
> +		/* Under sta2x11, DMA is there but limited to 512M */
> +		adev->dma_mask = SZ_512M - 1;
> +		adev->dev.coherent_dma_mask = SZ_512M - 1;
> +	}

This is pointless and unnecessary.  The PL011 driver itself doesn't use
_this_ struct device for anything to do with DMA at all.  That's all
handled by the DMA engine's struct device.

That's true of all APB devices.  Only AHB devices with a master port can
initiate bus transactions, and hence cause accesses to other parts of the
system.
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