linux-kernel - Re: [PATCH 5/4] ARM: footbridge: remove custom DMA address handling

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Date:   Thu, 25 Aug 2022 11:34:12 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH 5/4] ARM: footbridge: remove custom DMA address handling

On Thu, Aug 25, 2022 at 11:17:52AM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Footbridge is the last Arm platform that has its own
> __virt_to_bus()/__bus_to_virt()/phys_to_dma()/dma_to_phys() abstraction,
> but this is just a simple offset now.
> 
> For ISA DMA (floppy etc), the offset is actually zero, so the special
> hack to subtract the bus offset can be removed from common code.

No, the offset is definitely not zero for ISA devices. ISA devices have
the same view of system memory as PCI devices, since ISA devices go
through a southbridge and on to the PCI bus. So their view of the system
is exactly the same as any other PCI device.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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