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

[Vignesh Raghavendra]

On 02/07/19 11:23 PM, 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] 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@xxxxxx>
> [...]
> 
>    I have at least created my HyperBus driver and unfortunately I'm having serious
> issues with the design of the support core (see below)...
> 
> [...]
>> 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)
>> +{
>> +	const struct hyperbus_ops *ops;
>> +	struct hyperbus_ctlr *ctlr;
>> +	struct device_node *np;
>> +	struct map_info *map;
>> +	struct resource res;
>> +	struct device *dev;
>> +	int ret;
>> +
>> +	if (!hbdev || !hbdev->np || !hbdev->ctlr || !hbdev->ctlr->dev) {
>> +		pr_err("hyperbus: please fill all the necessary fields!\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	np = hbdev->np;
>> +	ctlr = hbdev->ctlr;
>> +	if (!of_device_is_compatible(np, "cypress,hyperflash"))
>> +		return -ENODEV;
>> +
>> +	hbdev->memtype = HYPERFLASH;
>> +
>> +	ret = of_address_to_resource(np, 0, &res);
> 
>    Hm, I doubt that the HB devices are wholly mapped into memory space, that seems
> like a property of the HB controller. In my case, the flash device in the DT has
> only single-cell "reg" prop (equal to the chip select #). Then this function returns 
> -EINVAL and the registration fails. Also, in my case such mapping is R/O, not R/W.
> 

You could declare R/O MMIO region in controla and set up a translation using ranges
from slave's reg CS based reg mapping like:

+	hbmc: hyperbus@47034000 {
+		compatible = "ti,am654-hbmc";
+		reg = <0x0 0x47034000 0x0 0x100>,
+			<0x5 0x00000000 0x1 0x0000000>;
+		#address-cells = <2>;
+		#size-cells = <1>;
+		ranges = <0x0 0x0 0x5 0x00000000 0x4000000>, /* CS0 - 64MB */
+			 <0x1 0x0 0x5 0x04000000 0x4000000>; /* CS1 - 64MB */
+
+		/* Slave flash node */
+		flash@0,0 {
+			compatible = "cypress,hyperflash", "cfi-flash";
+			reg = <0x0 0x0 0x4000000>;
+		};
+	};

If you use just CS# how would you handle CS to MMIO region mapping? 
Does both CS use the same MMIO base for reads?


>> +	if (ret)
>> +		return ret;
>> +
>> +	dev = ctlr->dev;
>> +	map = &hbdev->map;
>> +	map->size = resource_size(&res);
>> +	map->virt = devm_ioremap_resource(dev, &res);
>> +	if (IS_ERR(map->virt))
>> +		return PTR_ERR(map->virt);
> 
>    Again, I doubt that this should be done here, and not in the HB controller driver...

If multiple CS use same MMIO base, then I can make this part of code non fatal
when reg entry is a single cell and introduce notion of CS like SPI

> 
> [...]
> 
> MBR, Sergei
> 

-- 
Regards
Vignesh