linux-kernel - Re: [RFC PATCH 3/5] mtd: Add support for Hyperbus memory devices

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Message-ID: <a208a121-53a7-7d9a-c2db-ba135e17d3a0@cogentembedded.com>
Date:   Tue, 26 Feb 2019 14:08:35 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Vignesh R <vigneshr@...com>, David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Rob Herring <robh+dt@...nel.org>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "tudor.ambarus@...rochip.com" <tudor.ambarus@...rochip.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Nori, Sekhar" <nsekhar@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 3/5] mtd: Add support for Hyperbus memory devices

On 02/26/2019 01:26 PM, Vignesh R wrote:

>> [...]

>>>>> HyperBus specification can be found at[1]
>>>>> HyperFlash datasheet can be found at[2]
>>>>>
>>>>> [1] https://www.cypress.com/file/213356/download
>>>>> [2] https://www.cypress.com/file/213346/download
>>>>> [3] http://www.ti.com/lit/ug/spruid7b/spruid7b.pdf
>>>>>     Table 12-5741. HyperFlash Access Sequence
>>>>>
>>>>> Signed-off-by: Vignesh R <vigneshr@...com>
>> [...]
>>>>> diff --git a/drivers/mtd/hyperbus/core.c b/drivers/mtd/hyperbus/core.c
>>>>> new file mode 100644
>>>>> index 000000000000..d3d44aab7503
>>>>> --- /dev/null
>>>>> +++ b/drivers/mtd/hyperbus/core.c
>> [...]
>>>>> +		return -EINVAL;
>>>>> +
>>>>> +	dev = hbdev->dev;
>>>>> +	map = &hbdev->map;
>>>>> +	map->size = resource_size(&res);
>>>>> +	map->virt = devm_ioremap_resource(dev, &res);
>>>>> +	if (IS_ERR(map->virt))
>>>>> +		return PTR_ERR(map->virt);
>>>>> +
>>>>> +	map->name = dev_name(dev);
>>>>> +	map->bankwidth = 2;
>>>>> +
>>>>> +	simple_map_init(map);
>>>>
>>>>    It's not that simple, I'm afraid -- e.g. Renesas RPC-IF has read and write
>>>> mappings in the separate memory resources.
>>>>
>>>
>>> Hmm, could you point me to public datasheet of the controller?
>>
>>    See chapter 20 in [1]. Note that it's not the same SoC I'm developing for (R-Car
>> gen3 family, with NDA docs) but should be mostly the same RPC-IF core.
>>
>> [1] https://www.renesas.com/us/en/doc/products/mpumcu/doc/rz/r01uh0746ej0200-rza2m.pdf?key=74862185b5e22ad09e648d21a35de615
> 
> Thanks for the info!
> 
>>> simple_map_init() provides default implementation for map operations
>>> which is overridden, if hb_ops is populated.
>>> I think, Renesas RPC-IF can populate custom hb_ops struct and use
>>> appropriate MMIO base for read vs write, while still reusing the map
>>> framework. Wouldnt that work?
>>
>>    It probably would...
>
> Looking at above link, I see there are two HBMC controllers on Renesas
> SoC. One is a dedicated HBMC controller(chapter 21) very similar to that

   We don't have this one in the R-Car gen3 -- I wasn't even aware of it. :-)
RZ/A2 is newer than gen3 SoCs.

> on TI SoC and a SPI Multi I/O Bus Controller (chapter 20) that also
> supports Hyperbus protocol.

   That matches to the gen3 RPC-IF core.

> AFAICS, passing custom hb_ops is good enough to support both HW needs.
> Let me know if something is missing. I would greatly appreciate if you
> could test this series with your HW.

   Yes, I have stated the conversion from the simple mapping driver.

MBR, Sergei