netdev - Re: [PATCH] net: ethernet: renesas: sh_eth: do not access POST registers if not exist

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Date:   Tue, 30 Aug 2016 16:26:30 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Chris Brandt <Chris.Brandt@...esas.com>
Cc:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "David S . Miller" <davem@...emloft.net>,
        Simon Horman <horms+renesas@...ge.net.au>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Daniel Palmer <daniel@...f.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH] net: ethernet: renesas: sh_eth: do not access POST
 registers if not exist

Hi Chris,

On Tue, Aug 30, 2016 at 4:16 PM, Chris Brandt <Chris.Brandt@...esas.com> wrote:
> On Aug 29, 2016, Sergei Shtylyov wrote:
>>    SH7757 is not the only platform with TSU, there's e.g. R8A7740 ARM
>> SoC which only has 1 GETHER channel...
>
> I don't have the R8A7740 manual (R-Mobile A1) so I can't see. But even if it does not have the POST registers, it might not hurt anything.

R8a7740 does have the POST registers.

> I just looked at the RZ/A1 register space and there seems to be dummy registers in the POST1-4 area. I can write to them and read back what I wrote...which is all that the sh_eth driver cares about. I bet when the designers bring in the EtherC IP block, the entire register address is always populated with a simple latch registers. And then, if a feature is not included (like relay/POST), then nothing is hooked up on the back side of it.

What a waste of transistors...
There are plenty of hidden registers in many IP blocks.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds