linux-kernel - Re: [PATCH v7 1/2] spi: Add Renesas R-Car Gen3 RPC-IF SPI controller driver

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Date:   Sat, 26 Jan 2019 10:41:07 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     masonccyang@...c.com.tw
Cc:     bbrezillon@...nel.org, broonie@...nel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Simon Horman <horms@...ge.net.au>, juliensu@...c.com.tw,
        linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-spi@...r.kernel.org, sergei.shtylyov@...entembedded.com,
        zhengxunli@...c.com.tw
Subject: Re: [PATCH v7 1/2] spi: Add Renesas R-Car Gen3 RPC-IF SPI controller
 driver

On 1/24/19 7:28 AM, masonccyang@...c.com.tw wrote:
> Hi Marek,

Hi,

>> "Marek Vasut" <marek.vasut@...il.com>
>> 2019/01/24 上午 11:14
>> >>
>> >> > +module_platform_driver(rpc_spi_driver);
>> >>
>> >> RPC is not a SPI controller, it's a SPI and HF controller.
>> >>
>> >> Also, how difficult will it be to add the HF support ?
>> >
>> > One of my customers needs RPC SPI driver for our company's
>> > Octal-Flash,MX25UW51245G.
>> > We don't have HF product and hope you could understanding.
>>
>> I am worried that when we need to add RPC HF support (which is what all
>> boards but the D3 Draak use), we will have to rewrite the entire driver
>> and/or convert it to MFD and that would be a tremendous undertaking. I'd
>> prefer to have the driver ready for the HF addition before it's accepted
>> upstream.
>>
> 
> I think maybe your concerned would be happened only if HF driver goes with
> spi-mem layer.
> 
> A comment for HF from Daniel Fishman. FYR.
> 
> https://www.quora.com/What-is-a-hyper-flash-memory-and-how-is-it-different-from-normal-flash-memory

I have a decent idea what HF and SPI NOR are, since I wrote the RPC
driver for both HF and SPI mode for U-Boot (as I mentioned earlier).

The HF in Linux would use the CFI NOR part of MTD framework. My concern
is that when we need to add HF support into this driver, this driver
will have to be basically rewritten, since the architecture won't allow
for that. I'd like to avoid that, since the majority of Gen3 boards,
expect for the D3 Draak, use RPC in HF mode.

-- 
Best regards,
Marek Vasut