netdev - Re: [PATCH 2/3] net: socionext: Add Synquacer NetSec driver

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Date:   Thu, 30 Nov 2017 12:42:34 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     ard.biesheuvel@...aro.org
Cc:     dan.j.williams@...el.com, will.deacon@....com,
        jassisinghbrar@...il.com, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, arnd.bergmann@...aro.org,
        robh+dt@...nel.org, mark.rutland@....com,
        jaswinder.singh@...aro.org
Subject: Re: [PATCH 2/3] net: socionext: Add Synquacer NetSec driver

From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Date: Thu, 30 Nov 2017 17:37:27 +0000

> Well, the whole point of using memremap() instead of ioremap() is that
> the region has memory semantics, i.e., we read the MAC address and the
> DMA engine microcode from it. If memremap() itself is flawed in this
> regard, I agree we should fix it. But as I understand it, this is
> really an implementation problem in memremap() [the fact that it falls
> back to ioremap()] and not a problem in this driver.
> 
> So what alternative would you propose in this case?
> 
> BTW, this should be IOREMAP_WC not IOREMAP_WT, because the EEPROM on
> the platform in question does not tolerate cached mappings (or rather,
> shareable mappings). ioremap_wt() happens to result in device mappings
> rather than writethrough cacheable mappings, but this is another
> problem in itself. Once arm64 fixes ioremap_wt(), this code will no
> longer work on the SynQuacer SoC.

It doesn't "fall back", it directly uses ioremap_wt() for non-RAM
mappings.

It you look, most architectures do a "#define iomrep_wt ioremap"