netdev - Re: [PATCH] [v6] net: emac: emac gigabit ethernet controller driver

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Date:	Wed, 29 Jun 2016 10:46:23 -0500
From:	Timur Tabi <timur@...eaurora.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, sdharia@...eaurora.org,
	shankerd@...eaurora.org, vikrams@...eaurora.org,
	cov@...eaurora.org, gavidov@...eaurora.org, robh+dt@...nel.org,
	andrew@...n.ch, bjorn.andersson@...aro.org, mlangsdo@...hat.com,
	jcm@...hat.com, agross@...eaurora.org, davem@...emloft.net,
	f.fainelli@...il.com, catalin.marinas@....com
Subject: Re: [PATCH] [v6] net: emac: emac gigabit ethernet controller driver

Arnd Bergmann wrote:
> Usually drivers try 64-bit mask and 32-bit masks, and the 32 bit
> mask is practically guaranteed to succeed.

Sure, but in theory, my for-loop is correct, right?  Wouldn't there be 
some value in setting a 36-bit or 40-bit DMA mask if it works?  We have 
a platform where memory starts at a 40-bit address, so some devices have 
a 44-bit address bus.  If a 64-bit mask doesn't work, then a 32-bit mask 
certainly wont.

> Platforms will also allow allow the driver to set a mask that
> is larger than what the bus supports, as long as all RAM is
> reachable by the bus.

And that check (like all others) is made in the dma_set_mask call?

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