Message-ID: <9dbd8132-ce8f-9ce7-ddf5-d9826e2a1be1@cogentembedded.com>
Date:   Mon, 17 Jun 2019 22:45:45 +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:     linux-mtd@...ts.infradead.org,
        Tudor Ambarus <Tudor.Ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Joakim Tjernlund <Joakim.Tjernlund@...inera.com>,
        devicetree@...r.kernel.org, Mason Yang <masonccyang@...c.com.tw>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/5] mtd: Add support for HyperBus memory devices

Hello!

On 06/11/2019 02:57 PM, Vignesh Raghavendra wrote:

>>> 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>
>> [...]
>>> diff --git a/drivers/mtd/hyperbus/hyperbus-core.c b/drivers/mtd/hyperbus/hyperbus-core.c
>>> new file mode 100644
>>> index 000000000000..df1f75e10b1a
>>> --- /dev/null
>>> +++ b/drivers/mtd/hyperbus/hyperbus-core.c
>>> @@ -0,0 +1,191 @@
>>> +// 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
>>
>>    Mhm, I think I've already protested about this being #define'd here...
> 
> I thought you had agreed that default optional calibration routine can
> be part of core code and thus this #define.
> 
> Anyways, what is your preference here? Drop the constant and use a local
> variable in hyperbus_calibrate()?
> Or are you suggesting to move hyperbus_calibrate() TI's specific driver?

   I'm just not comfortable with the common HF code using quite an arbitrary
constant...

>> [...]
>>> diff --git a/include/linux/mtd/hyperbus.h b/include/linux/mtd/hyperbus.h
>>> new file mode 100644
>>> index 000000000000..ee2eefd822c9
>>> --- /dev/null
>>> +++ b/include/linux/mtd/hyperbus.h
>>> @@ -0,0 +1,91 @@
[...]
>>> + * @mtd: pointer to MTD struct
>>> + * @ctlr: pointer to HyperBus controller struct
>>> + * @memtype: type of memory device: HyperFlash or HyperRAM
>>> + * @registered: flag to indicate whether device is registered with MTD core
>>> + */
>>> +
>>> +struct hyperbus_device {
>>> +	struct map_info map;
>>> +	struct device_node *np;
>>> +	struct mtd_info *mtd;
>>> +	struct hyperbus_ctlr *ctlr;
>>> +	enum hyperbus_memtype memtype;
>>> +	bool registered;
>>> +};
>>> +
>>> +/**
>>> + * struct hyperbus_ops - struct representing custom HyperBus operations
>>> + * @read16: read 16 bit of data, usually from register/ID-CFI space
>>> + * @write16: write 16 bit of data, usually to register/ID-CFI space
>>
>>    Usually? How to differ the register/memory transfers if both are possible?

> CFI + map framework does not provide a way to differentiate b/w reg
> access vs memory access. read16()/write16() is used to either access
> registers or for sending various cmds like lock/unlock etc or for
> programming a single word.
> For regular read/writes copy_from() and copy_to() are used.

   In my case only copy_from() would exist -- no proper acceleration for
writes...

> Looking at HyperBus protocol, controllers would not need to
> differentiate b/w registers vs memory transfers for HyperFlash devices.
> So, I think I can drop read16/write16 and redirect these calls to
> copy_from()/copy_to()

   Doubt it, frankly speaking.

> I mainly added these functions keeping HyperRAM in mind. Idea was
> drivers would look at hyperbus_device->memtype and set to register
> access mode for HyperRAM in case of write16()/read16(). Looks like the
> interface is not intuitive enough
> So, will drop these and add it back when adding HyperRAM support.
> 
> Does that work for your HW as well?

   Don't think so...

   However, my HyperFlash driver could make use of the following #define's in
the HyperBus header:

#define HF_CMD_CA47		BIT(7)	/* Read */
#define HF_CMD_CA46		BIT(6)	/* Register space */
#define HF_CMD_CA45		BIT(5)	/* Linear burst */

#define HF_CMD_READ_REG		(HF_CMD_CA47 | HF_CMD_CA46)
#define HF_CMD_READ_MEM		HF_CMD_CA47
#define HF_CMD_WRITE_REG	HF_CMD_CA46
#define HF_CMD_WRITE_MEM	0

MBR, Sergei

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