Re: [PATCH RFT 0/2/2] mtd: hyperbus: add Renesas RPC-IF driver

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello!

On 02/18/2020 07:00 AM, Vignesh Raghavendra wrote:

>> Add the HyperFLash driver for the Renesas RPC-IF.  It's the "front end"
>> driver using the "back end" APIs in the main driver to talk to the real
>> hardware.
>>
>> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
[...]
>> Index: linux/drivers/mtd/hyperbus/rpc-if.c
>> ===================================================================
>> --- /dev/null
>> +++ linux/drivers/mtd/hyperbus/rpc-if.c
>> @@ -0,0 +1,162 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Linux driver for RPC-IF HyperFlash
>> + *
>> + * Copyright (C) 2019 Cogent Embedded, Inc.
>> + */
>> +
>> +#include <linux/err.h>
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/mtd/hyperbus.h>
>> +#include <linux/mtd/mtd.h>
>> +#include <linux/mux/consumer.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/types.h>
>> +
>> +#include <memory/renesas-rpc-if.h>
>> +
>> +struct	rpcif_hyperbus {
>> +	struct rpcif rpc;
>> +	struct hyperbus_ctlr ctlr;
>> +	struct hyperbus_device hbdev;
>> +};
>> +
>> +static const struct rpcif_op rpcif_op_tmpl = {
>> +	.cmd = {
>> +		.buswidth = 8,
>> +		.ddr = true,
>> +	},
>> +	.ocmd = {
>> +		.buswidth = 8,
>> +		.ddr = true,
>> +	},
>> +	.addr = {
>> +		.nbytes = 1,
>> +		.buswidth = 8,
>> +		.ddr = true,
>> +	},
>> +	.data = {
>> +		.buswidth = 8,
>> +		.ddr = true,
>> +	},
>> +};
>> +
> 
> Looking around, there seems to be more than one SPI controllers, apart
> from Renesas, which also support SPI NOR and HyperFlash protocol within
> a single IP block. E.g.: Cadence xSPI controller [1]. Therefore, we need
> a generic framework to support these kind of controllers.

   We can use e.g. 'struct rpcif_op' as generic command description.

> One way would be to extend spi_mem_op to support above template along
> with a new field to distinguish SPI NOR vs HyperFlash protocol. HyperBus
> core can then register a spi_device and use spi-mem ops to talk to
> controller driver.

   We have discussed this idea with Mark Brown, the SPI maintainer, and
he wasn't terribly impressed (I've invited him to #mtd -- his nick is
broonie and mine is headless, I'm also adding him to CC:).

> So, I suggest making Renesas RPC-IF backend a full fledged spi-mem
> driver (instead of driver/memory) and use extended spi_mem_op to support
> HyperFlash.

   I don't think cramming support for the different flash busses into
the SPI drivers is a good idea... I'm not against generalizing the
drivers/memory/ APIs though.

> [1]
> https://ip.cadence.com/uploads/1244/cdn-dsd-mem-fla-host-controller-ip-for-xspi-pdf

   Do they have the full datasheet available? I'll try looking at the driver 
tomorrow...

> Regards
> Vignesh

[removed the patch you haven't replied to]

MBR, Sergei

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