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

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello!

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

  Need space before (.

> 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.

   Communicating.

> Framework is modelled along the lines of spi-nor framework. HyperBus
> memory controller(HBMC) drivers call hb_register_device() to register a

   Again, space needed before (.

> 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

   Trying.

> flash as part of CFI flash probe.
> 
> HyperRAM is not supported atm.

   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/drivers/mtd/hyperbus/Kconfig b/drivers/mtd/hyperbus/Kconfig
> new file mode 100644
> index 000000000000..02c38afc5c50
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/Kconfig
> @@ -0,0 +1,23 @@
> +menuconfig MTD_HYPERBUS
> +	tristate "Hyperbus support"
> +	select MTD_CFI
> +	select MTD_MAP_BANK_WIDTH_2
> +	select MTD_CFI_AMDSTD
> +	select MTD_COMPLEX_MAPPINGS
> +	help
> +	  This is the framework for the Hyperbus which can be used by
> +	  the Hyperbus Controller driver to commmunicate with
                                              ^^^
  Too many m's. :-)

> +	  Hyperflash. See Cypress Hyperbus specification for more
> +	  details
> +
> +
> +if MTD_HYPERBUS
> +
> +config HBMC_AM654
> +	tristate "Hyperbus controller driver for AM65x SoC"
> +	help
> +	 This is the driver for Hyperbus controller on TI's AM65x and
> +	 other SoCs
> +
> +endif # MTD_HYPERBUS

  The above clearly belongs to patch #5.

> +

   No empty lines at end of file, please...

> diff --git a/drivers/mtd/hyperbus/Makefile b/drivers/mtd/hyperbus/Makefile
> new file mode 100644
> index 000000000000..64e377d7f636
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/Makefile
> @@ -0,0 +1,4 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_MTD_HYPERBUS)	+= core.o
> +obj-$(CONFIG_HBMC_AM654)	+= hbmc_am654.o

   The above line clearly belongs to patch #5 as well...

> diff --git a/drivers/mtd/hyperbus/core.c b/drivers/mtd/hyperbus/core.c
> new file mode 100644
> index 000000000000..d3d44aab7503
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/core.c
> @@ -0,0 +1,167 @@
> +// SPDX-License-Identifier: GPL-2.0
> +//
> +// Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> +// Author: Vignesh R <vigneshr@ti.com>
> +
> +#include <linux/err.h>
> +#include <linux/kernel.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 HB_CALIB_COUNT 25

   Isn't this controller specific?

[...]
> +/* Calibrate HBMC by repeatedly reading "QRY" string from CFI space */
> +static int hb_calibrate(struct hb_device *hbdev)

   s/int/bool/, perhaps?

[...]
> +int hb_register_device(struct hb_device *hbdev)
> +{
> +	struct resource res;
> +	struct device *dev;
> +	struct device_node *np;
> +	struct map_info *map;
> +	struct hb_ops *ops;
> +	int err;
> +
> +	if (!hbdev || !hbdev->dev || !hbdev->np) {
> +		pr_err("hyperbus: please fill all the necessary fields!\n");
> +		return -EINVAL;
> +	}
> +
> +	np = hbdev->np;
> +	if (!of_device_is_compatible(np, "cypress,hyperflash"))
> +		return -ENODEV;
> +
> +	hbdev->memtype = HYPERFLASH;
> +
> +	if (of_address_to_resource(np, 0, &res))

    Isn't the direct mapping property of the HF controller, not of HyperFlash
itself?

> +		return -EINVAL;
> +
> +	dev = hbdev->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);
> +
> +	map->name = dev_name(dev);
> +	map->bankwidth = 2;
> +
> +	simple_map_init(map);

   It's not that simple, I'm afraid -- e.g. Renesas RPC-IF has read and write
mappings in the separate memory resources.

[...]
> +	if (hbdev->needs_calib) {
> +		err = hb_calibrate(hbdev);
> +		if (!err) {

   Why call this variable 'err' when it indicates successful calibration?

> +			dev_err(hbdev->dev, "Calibration failed\n");
> +			return -ENODEV;
> +		}
> +	}
> +
> +	hbdev->mtd = do_map_probe("cfi_probe", map);
> +	if (!hbdev->mtd) {
> +		dev_err(hbdev->dev, "probing failed\n");

   "map probe", perhaps?

> +		return -ENXIO;
> +	}
> +
> +	hbdev->mtd->dev.parent = hbdev->dev;
> +	mtd_set_of_node(hbdev->mtd, np);
> +
> +	err = mtd_device_register(hbdev->mtd, NULL, 0);
> +	if (err) {
> +		dev_err(hbdev->dev, "failed to register mtd device\n");
> +		goto err_destroy;
> +	}
> +	hbdev->registered = true;
> +
> +	return 0;
> +
> +err_destroy:

   The label and the code below doesn't seem necessary. Just do it above
instead of *goto*.

> +	map_destroy(hbdev->mtd);
> +	return err;
> +}
[...]
> 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 {

   I'm for the full hyperbus_ prefixes, it's not that long and seems clearer.

[...]

MBR, Sergei