linux-kernel - Re: [PATCH v7 3/5] mtd: Add support for HyperBus memory devices

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Message-ID: <1131067e-a86d-f794-f6ae-be0a2b3e5832@ti.com>
Date:   Wed, 26 Jun 2019 11:30:56 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     <masonccyang@...c.com.tw>
CC:     Boris Brezillon <bbrezillon@...nel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Rob Herring <robh+dt@...nel.org>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Subject: Re: [PATCH v7 3/5] mtd: Add support for HyperBus memory devices



On 26/06/19 6:46 AM, masonccyang@...c.com.tw wrote:
> Hi Vignesh,
> 
>>
>> Subject
>>
>> [PATCH v7 3/5] mtd: Add support for HyperBus memory devices
>>
>> Cypress' HyperBus is Low Signal Count, High Performance Double Data Rate
>> Bus interface between a host system master and one or more slave
>> interfaces. HyperBus is used to connect microprocessor, microcontroller,
>> or ASIC devices with random access NOR flash memory (called HyperFlash)
>> or self refresh DRAM (called HyperRAM).
>>
>> Its a 8-bit data bus (DQ[7:0]) with  Read-Write Data Strobe (RWDS)
>> signal and either Single-ended clock(3.0V parts) or Differential clock
>> (1.8V parts). It uses ChipSelect lines to select b/w multiple slaves.
>> At bus level, it follows a separate protocol described in HyperBus
>> specification[1].
>>
>> HyperFlash follows CFI AMD/Fujitsu Extended Command Set (0x0002) similar
>> to that of existing parallel NORs. Since HyperBus is x8 DDR bus,
>> its equivalent to x16 parallel NOR flash wrt bits per clock cycle. But
>> HyperBus operates at >166MHz frequencies.
>> HyperRAM provides direct random read/write access to flash memory
>> array.
>>
>> But, HyperBus memory controllers seem to abstract implementation details
>> and expose a simple MMIO interface to access connected flash.
>>
>> Add support for registering HyperFlash devices with MTD framework. MTD
>> maps framework along with CFI chip support framework are used to support
>> communicating with flash.
>>
>> Framework is modelled along the lines of spi-nor framework. HyperBus
>> memory controller (HBMC) drivers calls hyperbus_register_device() to
>> register a single HyperFlash device. HyperFlash core parses MMIO access
>> information from DT, sets up the map_info struct, probes CFI flash and
>> registers it with MTD framework.
>>
>> Some HBMC masters need calibration/training sequence[3] to be carried
>> out, in order for DLL inside the controller to lock, by reading a known
>> string/pattern. This is done by repeatedly reading CFI Query
>> Identification String. Calibration needs to be done before trying to 
> detect
>> flash as part of CFI flash probe.
>>
>> HyperRAM is not supported at the moment.
>>
>> 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 Raghavendra <vigneshr@...com>
> 
> Cypress has announced the inclusion of Cypress’ high-bandwidth 
> HyperBus™ 8-bit serial memory interface into the new eXpanded SPI (xSPI) 
> electrical interface standard from the JEDEC Solid State Technology 
> Association 
> 
> for detail, please goes to
> https://www.cypress.com/news/cypress-hyperbus-memory-interface-instant-applications-incorporated-jedec-xspi-electrical 
> 

Thanks for the link!
Announcement seems to be from March 2018 since then Cypress has
published detailed HyperBus protocol in public domain . Comparing JEDEC
xSPI specification and HyperBus protocol that Cypress has published,
they seem to be following 8D-8D-8D Profile 2.0 with Extended Command
Modifier of JEDEC xSPI spec.
Did you see anything missing/different?

I need to study xSPI spec in more detail, but seems like as long as we
support HyperBus Protocol spec from Cypress we should be safe.

-- 
Regards
Vignesh