netdev - Re: [PATCH 2/2] sh_eth: remove 'register_type' field from 'struct sh_eth_plat

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Date:	Wed, 21 Aug 2013 14:58:25 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, lethal@...ux-sh.org,
	linux-sh@...r.kernel.org
Subject: Re: [PATCH 2/2] sh_eth: remove 'register_type' field from 'struct sh_eth_plat_data'

Hi Sergei,

On Wednesday 21 August 2013 16:49:52 Sergei Shtylyov wrote:
> On 21-08-2013 4:39, Laurent Pinchart wrote:
> >>>>>>> Now that the 'register_type' field of the 'sh_eth' driver's platform
> >>>>>>> data is not used by the driver anymore, it's time to remove it and
> >>>>>>> its initializers from the SH platform code. Also  move *enum*
> >>>>>>> declaring values for this  field from <linux/sh_eth.h>  to  the 
> >>>>>>> local driver's header file as they're only needed by the driver
> >>>>>>> itself now...
> >>>>>>> 
> >>>>>>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
> >>>> 
> >>>> [...]
> >>>> 
> >>>>>>>     /* Driver's parameters */
> >>>>>>>     #if defined(CONFIG_CPU_SH4) || defined(CONFIG_ARCH_SHMOBILE)
> >>>>>>>     #define SH4_SKB_RX_ALIGN    32
> >>>>>>> 
> >>>>>>> Index: net-next/include/linux/sh_eth.h
> >>>>>>> ===================================================================
> >>>>>>> --- net-next.orig/include/linux/sh_eth.h
> >>>>>>> +++ net-next/include/linux/sh_eth.h
> >>>>>>> @@ -5,17 +5,10 @@
> >>>>>>> 
> >>>>>>>     #include <linux/if_ether.h>
> >>>>>>>     
> >>>>>>>     enum {EDMAC_LITTLE_ENDIAN, EDMAC_BIG_ENDIAN};
> >>>>>>> 
> >>>>>>> -enum {
> >>>>>>> -    SH_ETH_REG_GIGABIT,
> >>>>>>> -    SH_ETH_REG_FAST_RCAR,
> >>>>>>> -    SH_ETH_REG_FAST_SH4,
> >>>>>>> -    SH_ETH_REG_FAST_SH3_SH2
> >>>>>>> -};
> >>>>>>> 
> >>>>>>>     struct sh_eth_plat_data {
> >>>>>>>     
> >>>>>>>         int phy;
> >>>>>>>         int edmac_endian;
> >>>>>> 
> >>>>>> Wouldn't it make sense to move the edmac_endian field to
> >>>>>> sh_eth_cpu_data as well ?
> >>>>> 
> >>>>> No, it depends on the SoC endianness which is determined by power-on
> >>>>> pin strapping -- which is board specific.
> >>> 
> >>> Does SoC endianness affect the ARM core endianness, the ethernet
> >>> registers endianness, or both ?
> >> 
> >> Both, AFAIK.
> >> 
> >>> If it affects the ARM core endianness only, the kernel needs to be
> >>> compiled in little-endian or big-endian mode anyway, and the sh_eth
> >>> driver should use cpu_to_le32() unconditionally. If it affects both the
> >>> ARM core and the ethernet controller there's not need to care about the
> >>> endianness, as it will always be good.
> >> 
> >> No, it won't unless you're using __raw_{readl|writel}() accessors. The
> >> driver doesn't do it. {readl|writel}() and io{read|write}32() that use
> >> them always assume LE ordering of memory.
> >> 
> >>> We only need to care about it if it affects the ethernet controller
> >>> registers only, which would seem weird to me.
> >> 
> >> Unfortunately, you are wrong.
> > 
> > Care to explain *why* ? There might be bugs in the driver (such as using
> > the wrong I/O accessors), but I don't see why we need to configure the
> > endianness through platform data.
> 
> Re-read my reply about the power-on pin strapping please. The SoC endianness
> setting gets read from the external source to the SoC, i.e. it's determined
> by the board.

Unless that pin doesn't affect the CPU core (in which case I wonder what it's 
used for), the kernel will need to be compiled for the specified endianness 
anyway. Endianness conversion can thus be performed with cpu_to_* (if the 
registers endianness is fixed) or skipped completely (if the registers 
endianness is also configured by the bootstrap pin) by using raw I/O 
accessors. Modifications will be need in the sh_eth driver, but I don't see 
why the driver would need to receive endianness information from platform data 
or DT.

-- 
Regards,

Laurent Pinchart

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