netdev - Re: [PATCH net-next 6/9] net: phy: add backplane kr driver support

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Date:   Fri, 24 Apr 2020 12:14:05 +0000
From:   Florinel Iordache <florinel.iordache@....com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "corbet@....net" <corbet@....net>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 6/9] net: phy: add backplane kr driver support

> On 3/26/2020 6:07 PM, Andrew Lunn wrote:
> >> +static u32 le_ioread32(void __iomem *reg) {
> >> +    return ioread32(reg);
> >> +}
> >> +
> >> +static void le_iowrite32(u32 value, void __iomem *reg) {
> >> +    iowrite32(value, reg);
> >> +}
> >> +
> >> +static u32 be_ioread32(void __iomem *reg) {
> >> +    return ioread32be(reg);
> >> +}
> >> +
> >> +static void be_iowrite32(u32 value, void __iomem *reg) {
> >> +    iowrite32be(value, reg);
> >> +}
> >
> > This is very surprising to me. I've not got my head around the
> > structure of this code yet, but i'm surprised to see memory mapped
> > access functions in generic code.
> 
> This abstraction makes no sense whatsoever, you already have
> io{read,write}32{be,} to deal with the correct endian, and you can use the
> standard Device Tree properties 'big-endian', 'little-endian', 'native-endian' to
> decide which of those of to use. If you need to introduce a wrapper or indirect
> function calls to select the correct I/O accessor, that is fine of course.
> --
> Florian

Hi Florian,
I need these wrappers in generic code in order to automatically assign the proper
I/O accessor in the following structure according to endianness specified in DT.

/* Endianness specific memory I/O */
struct mem_io {
	u32 (*read32)(void __iomem *addr);
	void (*write32)(u32 value, void __iomem *addr);
};

And then the usage is straightforward in device specific code:
io.read32(&reg_base->tcsr3) ...
io.write32((io.read32(&reg_base->tcsr1) ... 

without the need to check endianness at each call and select which read/write function to use.
This is done in order to reduce the overall number of LOC (lines of code).

Florin.