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SubjectRe: [PATCH v8 3/5] mtd: Add support for HyperBus memory devices

On 12/07/19 12:56 AM, Sergei Shtylyov wrote:
> Hello!
> On 06/25/2019 10:57 AM, 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 with respect to 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]
>> [2]
>> [3]
>> Table 12-5741. HyperFlash Access Sequence
>> Signed-off-by: Vignesh Raghavendra <>
> [...]
>> diff --git a/drivers/mtd/hyperbus/hyperbus-core.c b/drivers/mtd/hyperbus/hyperbus-core.c
>> new file mode 100644
>> index 000000000000..63a9e64895bc
>> --- /dev/null
>> +++ b/drivers/mtd/hyperbus/hyperbus-core.c
>> @@ -0,0 +1,154 @@
> [...]
>> +int hyperbus_register_device(struct hyperbus_device *hbdev)
>> +{
> [...]
>> + map->name = dev_name(dev);
>> + map->bankwidth = 2;
> I think this should really be 1, judging on the comment to that field (and on
> Cogent's own RPC-IF HF driver).

I agree this setting is a bit confusing because DDR nature. What we have
with HyperFlash in DDR mode is equivalent to 16bit flash on a 8bit bus
and kind of equal to 2 bus cycles (in this case clock edges), therefore
bandwidth would turn out to be 2. Otherwise cfi_build_cmd() would
generate wrong addresses and simple map implmention of read/writes would
use wrong accessors.
Only way I see map->bankwidth = 1 working is if HF is used in SDR mode.
So is Cogent's HF in SDR mode? I thought HyperFlash is DDR only but I
may be wrong.

>> + map->device_node = np;
> [...]
> MBR, Sergei


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