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

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Message-Id: <20171130.122917.542712364953497229.davem@davemloft.net>
Date:   Thu, 30 Nov 2017 12:29:17 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     jassisinghbrar@...il.com
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        arnd.bergmann@...aro.org, ard.biesheuvel@...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: jassisinghbrar@...il.com
Date: Thu, 30 Nov 2017 21:43:16 +0530

> +	priv->eeprom_base = devm_memremap(&pdev->dev, eeprom_res->start,
> +					  resource_size(eeprom_res),
> +					  MEMREMAP_WT);
> +	if (!priv->eeprom_base) {
> +		dev_err(&pdev->dev, "devm_memremap() failed for EEPROM\n");
> +		ret = -ENXIO;
> +		goto free_ndev;
> +	}

dev_memremap() is implemented via memremap() which for MEMREMAP_WT is
in turn implemented using ioremap_wt() which returns an "__iomem"
pointer.

The memremap() function talks about __iomem being about side effects.
That's not really the full story.  The __iomem annotation is also
about whether a special accessor is necessary to "dereference" the
pointer.  On sparc64, for example, the ioremap_*() functions return a
physical address not a virtual one.  So you cannot directly
dereference pointers that are returned from the ioremap*() interfaces.

You'll also need to mark priv->eeprom_base as "__iomem".

devm_memremap() returns a straight "void *" without the __iomem
annotation, and this is wrong then ioremap_*() is used.