linux-kernel - RE: [RESEND PATCH] arm: Enlarge IO_SPACE

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Message-ID: <4f6e5115e00e4df2a84a57ed0359e907@AcuMS.aculab.com>
Date:   Sun, 9 May 2021 16:54:51 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Russell King - ARM Linux admin' <linux@...linux.org.uk>,
        Ansuel Smith <ansuelsmth@...il.com>
CC:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RESEND PATCH] arm: Enlarge IO_SPACE_LIMIT needed for some SoC

...
> Well, an obvious question would be: do you really need that much IO
> space? PCs have got away with 64K of IO space without having a problem
> for years, so 64K per bus should be fine. If you have 3 buses, that
> should be 3 * 64K or 192K.

Not only that, but most modern PCI (even) cards don't require IO space.
Or does this include memory space - which can be much bigger.

I have cut one of our FPGA PCIe slaves down from two 8MB BARs to
two 1MB ones, with the extra small BARs (eg for MSI-X) the bridge
would have allocated 32MB, now 4MB.
Fortunately that card only needs to work on x86-64.

	David

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