linux-kernel - Re: [PATCH v2 0/7] Add support for Exynos SROM Controller driver

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Date:	Tue, 06 Oct 2015 09:23:42 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Pavel Fedin <p.fedin@...sung.com>,
	'Pankaj Dubey' <pankaj.dubey@...sung.com>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Cc:	k.kozlowski.k@...il.com, thomas.ab@...sung.com, kgene@...nel.org,
	heiko@...ech.de
Subject: Re: [PATCH v2 0/7] Add support for Exynos SROM Controller driver

On 05.10.2015 22:18, Pavel Fedin wrote:
>  Hello!
> 
>> That is interesting. What do you mean by that? Although SROM controller
>> can access external memory (SRAM, ROM) but it is not exactly a bus. How
>> is the SMSC9111 "connected"? What interface or protocol is used?
> 
>  SROM controller actually provides a demultiplexed external address and data bus. This way you could
> hook up old good ROM chip to it (hence its name). However, you can plug in there anything else with
> the appropriate interface, and SMSC9111 uses exactly that. Just some address + control + data wires.
> Therefore, you can think of SROMc as a simple bus.

Ah, okay, thanks for details.

> 
>> I am sorry but I cannot figure out what exactly are you talking about.
>> The Device Tree is the glue to describe the board, the hardware and its
>> configuration. Please elaborate a little more.
> 
>  Yes, exactly that. SROM controller has 4 outputs, and for every of these outputs you have to choose
> mode and timings. Once you set them correctly, you can use peripherial behind them. These timings
> actually depend on the actual peripherial.
> 
>  By this time i remembered that u-boot guys also did something with this. And here are links:
> http://git.denx.de/?p=u-boot.git;a=blob;f=arch/arm/dts/exynos5250-smdk5250.dts;h=8b695442b1a29dec4e3
> 53ebd3cfee0ff89f218a6;hb=HEAD#l43 - this is how connection is described
> http://git.denx.de/?p=u-boot.git;a=blob;f=board/samsung/common/board.c;h=d32c75de50858f131284e28db0c
> 7ed55883f1cb0;hb=HEAD#l184 - and this is parsing code

I see... Pankaj's driver was not developed for that purpose. You would
have to extend it. For the SROMC driver there shouldn't be much work to
do: just parse additional bindings and configure the controller for
ethernet adapter.

>  There's only one small problem with their code. "bank" parameter is device-wide, therefore you
> cannot configure more than one bank. For SMDK boards it's OK, but in future you may run into problem
> with this.

You are not bound by u-boot bindings anyhow (at least to my
understanding). You can try to re-use them but if some binding is
problematic then just create your own.

Best regards,
Krzysztof

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