linux-kernel - Re: [RFC PATCH v2 3/5] mtd: Add support for Hyperbus memory devices

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Message-ID: <02dfcf5d-f7f8-f33a-22b2-462ea92b0702@cogentembedded.com>
Date:   Tue, 26 Mar 2019 10:51:23 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Vignesh Raghavendra <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:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, linux-mtd@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, tudor.ambarus@...rochip.com,
        nsekhar@...com, Mason Yang <masonccyang@...c.com.tw>
Subject: Re: [RFC PATCH v2 3/5] mtd: Add support for Hyperbus memory devices

On 25.03.2019 23:13, Sergei Shtylyov wrote:

>> Cypress' Hyperbus is Low Signal Count, High Performance Double Data Rate
> 
>     It's HyperBus, according to the spec...
> 
>> 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].
> 
>     HyperBus.
>> 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
> 
>     HyperBus.
> 
>> and expose a simple MMIO interface to access connected flash.
>>
>> Add support for registering Hyperflash devices with MTD framework. MTD
> 
>     HyperFlash.
> 
>> 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
> 
>     HyperBus.
> 
>> memory controller (HBMC) drivers calls hyperbus_register_device() to
>> register a single Hyperflash device. Hyperflash core parses MMIO access
> 
>     HyperFlash.
> 
>> 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]
> 
>    HyperBus & HyperFlash.
>   
>> [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>
> [...]
>> diff --git a/drivers/mtd/hyperbus/hyperbus-core.c b/drivers/mtd/hyperbus/hyperbus-core.c
>> new file mode 100644
>> index 000000000000..4c2876c367fc
>> --- /dev/null
>> +++ b/drivers/mtd/hyperbus/hyperbus-core.c
>> @@ -0,0 +1,183 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +//
>> +// Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
>> +// Author: Vignesh Raghavendra <vigneshr@...com>
>> +
>> +#include <linux/err.h>
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/mtd/hyperbus.h>
>> +#include <linux/mtd/map.h>
>> +#include <linux/mtd/mtd.h>
>> +#include <linux/mtd/cfi.h>
>> +#include <linux/of.h>
>> +#include <linux/of_address.h>
>> +#include <linux/types.h>
>> +
>> +#define HYPERBUS_CALIB_COUNT 25
> 
>     As I said, this seems platform specific...
> 
> [...]
>> +/* Default calibration routine for use by Hyperbus controller.
> 
>     No, there should be easy opt-out from the calibration method.
> Currently, the driver will have to define its own calibrate method, even
> if does't need any calibration...

    Nevermind -- the method ptr can be NULL, of course, so there's easy opt-out...

[...]

MBR, Sergei