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

[Vignesh Raghavendra <vigneshr@ti.com>]

On 26/02/19 11:46 PM, Sergei Shtylyov wrote:
> On 02/19/2019 09:36 AM, Vignesh R (by way of Boris Brezillon <bbrezillon@kernel.org>) 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 clk. 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
>> communicate with flash.
>>
>> Framework is modelled along the lines of spi-nor framework. HyperBus
>> memory controller(HBMC) drivers call hb_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 try to detect
>> flash as part of CFI flash probe.
>>
>> HyperRAM is not supported atm.
>>
>> 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@ti.com>
> [...]
>> diff --git a/include/linux/mtd/hyperbus.h b/include/linux/mtd/hyperbus.h
>> new file mode 100644
>> index 000000000000..0aa11458c424
>> --- /dev/null
>> +++ b/include/linux/mtd/hyperbus.h
>> @@ -0,0 +1,73 @@
>> +/* SPDX-License-Identifier: GPL-2.0
>> + *
>> + * Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
>> + */
>> +
>> +#ifndef __LINUX_MTD_HYPERBUS_H__
>> +#define __LINUX_MTD_HYPERBUS_H__
>> +
>> +#include <linux/mtd/map.h>
>> +
>> +enum hb_memtype {
>> +	HYPERFLASH,
>> +	HYPERRAM,
>> +};
>> +
>> +/**
>> + * struct hb_device - struct representing Hyperbus slave device
>> + * @map: map_info struct for accessing MMIO Hyperbus flash memory
>> + * @dev: device pointer of Hyperbus Controller
> 
>    I think we need a separate structure for the HyperBus controller, not just
> for the slave devices...
> 
>> + * @np:	pointer to Hyperbus slave device node
>> + * @mtd: pointer to MTD struct
>> + * @ops: pointer to custom Hyperbus ops
>> + * @memtype: type of memory device: Hyperflash or HyperRAM
>> + * @needs_calib: flag to indicate whether calibration sequence is needed
>> + * @registered: flag to indicate whether device is registered with MTD core
>> + */
>> +
>> +struct hb_device {
>> +	struct map_info map;
>> +	struct device *dev;
>> +	struct device_node *np;
>> +	struct mtd_info *mtd;
>> +	struct hb_ops *ops;
>> +	enum hb_memtype memtype;
>> +	bool needs_calib;
>> +	bool registered;
>> +};
>> +
>> +/**
>> + * struct hb_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
>> + * copy_from: copy data from flash memory
>> + * copy_to: copy data to flash_memory
>> + */
>> +
>> +struct hb_ops {
>> +	u16 (*read16)(struct hb_device *hbdev, unsigned long addr);
>> +	void (*write16)(struct hb_device *hbdev, unsigned long addr, u16 val);
>> +
>> +	void (*copy_from)(struct hb_device *hbdev, void *to,
>> +			  unsigned long from, ssize_t len);
>> +	void (*copy_to)(struct hb_device *dev, unsigned long to,
>> +			const void *from, ssize_t len);
> 
>    ... else these methods won't fly if you need to "massage" the controller
> registers inside them...
> 

If accessing controller register is the only need, wouldn't a private
data pointer within struct hb_device be sufficient to hold pointer to
controller specific struct?

struct hb_device {
	...
	void *priv; /* points to controller's private data */
};


Or do you see a need for separate structure for the HyperBus controller?


>> +};
> [...]
> 
> MBR, Sergei
> 

-- 
Regards
Vignesh