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SubjectRe: [PATCH v4 10/21] mtd: support BB SRAM on ICP DAS LP-8x4x
Hi Sergei,

A few more small comments.

On Wed, Apr 16, 2014 at 09:17:15PM +0400, Sergei Ianovich wrote:
> This provides an MTD device driver for 512kB of battery backed up SRAM
> on ICPDAS LP-8X4X programmable automation controllers.
>
> SRAM chip is connected via FPGA and is not accessible without a driver,
> unlike flash memory which is wired to CPU MMU.
>
> This SRAM becomes an excellent persisent storage of volatile process
> data like counter values and sensor statuses. Storing those data in
> flash or mmc card is not a viable solution.
>
> Signed-off-by: Sergei Ianovich <ynvich@gmail.com>
> Reviewed-by: Brian Norris <computersforpeace@gmail.com>
> ---
> v3..v4 for Brian Norris 'Reviewed-by'
> * add doc file for DT binding
> * move DTS binding to a different patch (8/21)
> * drop unused include directive
> * drop safely unused callback
> * drop non-default partion probe types
> * drop duplicate error checks
> * drop duplicate error reporting
> * fixed error message on MTD registeration
> * fixed module removal routine

Thanks for the updates. This patch looks pretty good to me.

> v2..v3
> * no changes (except number 08/16 -> 10/21)
>
> v0..v2
> * use device tree
> * use devm helpers where possible
>
> .../devicetree/bindings/mtd/sram-lp8x4x.txt | 22 +++
> arch/arm/configs/lp8x4x_defconfig | 1 +
> drivers/mtd/devices/Kconfig | 14 ++
> drivers/mtd/devices/Makefile | 1 +
> drivers/mtd/devices/sram_lp8x4x.c | 204 +++++++++++++++++++++
> 5 files changed, 242 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/mtd/sram-lp8x4x.txt
> create mode 100644 drivers/mtd/devices/sram_lp8x4x.c
>
> diff --git a/Documentation/devicetree/bindings/mtd/sram-lp8x4x.txt b/Documentation/devicetree/bindings/mtd/sram-lp8x4x.txt
> new file mode 100644
> index 0000000..8b1e864
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/mtd/sram-lp8x4x.txt
> @@ -0,0 +1,22 @@
> +512kB battery backed up SRAM on LP-8x4x industrial computers
> +
> +Required properties:
> +- compatible : should be "icpdas,sram-lp8x4x"
> +
> +- reg: physical base addresses and region lengths of
> + * IO memory range
> + * SRAM page selector

Are these region types pretty static for this type of hardware? If not,
it helps to have a reg-names property in the DT, when there are 2 or
more register resources.

> +- eeprom-gpios : should point to active-low write enable GPIO

I'm curious: your driver doesn't actually utilize this binding. Is this
intentional? Is it actually optional? (I note that the example DT below
doesn't have this property...)

> +
> +SRAM chip is connected via FPGA and is not accessible without a driver,
> +unlike flash memory which is wired to CPU MMU. Driver is essentially
> +an address translation routine.
> +
> +Example:
> +
> + sram@a000 {
> + compatible = "icpdas,sram-lp8x4x";
> + reg = <0xa000 0x1000
> + 0x901e 0x1>;
> + };
> diff --git a/arch/arm/configs/lp8x4x_defconfig b/arch/arm/configs/lp8x4x_defconfig
> index d60e37a..17a4e6f 100644
> --- a/arch/arm/configs/lp8x4x_defconfig
> +++ b/arch/arm/configs/lp8x4x_defconfig
> @@ -57,6 +57,7 @@ CONFIG_MTD_CFI_ADV_OPTIONS=y
> CONFIG_MTD_CFI_GEOMETRY=y
> CONFIG_MTD_CFI_INTELEXT=y
> CONFIG_MTD_PHYSMAP_OF=y
> +CONFIG_MTD_SRAM_LP8X4X=y
> CONFIG_PROC_DEVICETREE=y
> CONFIG_BLK_DEV_LOOP=y
> CONFIG_BLK_DEV_LOOP_MIN_COUNT=2

I can't take the defconfig update via MTD; it will need to go via the
appropriate ARM tree (arm-soc?). So this hunk needs to move to another
patch.

> diff --git a/drivers/mtd/devices/Kconfig b/drivers/mtd/devices/Kconfig
> index 1210bc2..fc8552b 100644
> --- a/drivers/mtd/devices/Kconfig
> +++ b/drivers/mtd/devices/Kconfig
> @@ -225,4 +225,18 @@ config BCH_CONST_T
> default 4
> endif
>
> +config MTD_SRAM_LP8X4X
> + tristate "SRAM on ICPDAS LP-8X4X"
> + depends on OF && ARCH_PXA
> + ---help---
> + This provides an MTD device driver for 512kiB of battery backed up SRAM
> + on ICPDAS LP-8X4X programmable automation controllers.
> +
> + SRAM chip is connected via FPGA and is not accessible without a driver,
> + unlike flash memory which is wired to CPU MMU.
> +
> + Say N, unless you plan to run this kernel on LP-8X4X.
> +
> + If you say M, the module will be called sram_lp8x4x.
> +
> endmenu
> diff --git a/drivers/mtd/devices/Makefile b/drivers/mtd/devices/Makefile
> index c68868f..a7d86e2 100644
> --- a/drivers/mtd/devices/Makefile
> +++ b/drivers/mtd/devices/Makefile
> @@ -17,6 +17,7 @@ obj-$(CONFIG_MTD_SPEAR_SMI) += spear_smi.o
> obj-$(CONFIG_MTD_SST25L) += sst25l.o
> obj-$(CONFIG_MTD_BCM47XXSFLASH) += bcm47xxsflash.o
> obj-$(CONFIG_MTD_ST_SPI_FSM) += st_spi_fsm.o
> +obj-$(CONFIG_MTD_SRAM_LP8X4X) += sram_lp8x4x.o
>
>
> CFLAGS_docg3.o += -I$(src)
> diff --git a/drivers/mtd/devices/sram_lp8x4x.c b/drivers/mtd/devices/sram_lp8x4x.c
> new file mode 100644
> index 0000000..4cfa70b
> --- /dev/null
> +++ b/drivers/mtd/devices/sram_lp8x4x.c
> @@ -0,0 +1,204 @@
> +/*
> + * linux/drivers/mtd/devices/lp8x4x_sram.c
> + *
> + * MTD Driver for SRAM on ICPDAS LP-8x4x
> + * Copyright (C) 2013 Sergei Ianovich <ynvich@gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation or any later version.
> + */
> +
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/mtd/map.h>
> +#include <linux/mtd/mtd.h>
> +#include <linux/mtd/partitions.h>
> +#include <linux/platform_device.h>
> +#include <linux/of_device.h>
> +#include <linux/slab.h>
> +#include <linux/string_helpers.h>
> +#include <linux/types.h>
> +
> +struct lp8x4x_sram_info {
> + void __iomem *bank;
> + void __iomem *virt;
> + struct mutex lock;
> + unsigned active_bank;
> + struct mtd_info mtd;
> +};
> +
> +static int
> +lp8x4x_sram_erase(struct mtd_info *mtd, struct erase_info *instr)
> +{
> + struct lp8x4x_sram_info *info = mtd->priv;
> + unsigned bank = instr->addr >> 11;
> + unsigned offset = (instr->addr & 0x7ff) << 1;
> + loff_t i;
> +
> + mutex_lock(&info->lock);
> + if (unlikely(bank != info->active_bank)) {
> + info->active_bank = bank;
> + iowrite8(bank, info->bank);
> + }
> + for (i = 0; i < instr->len; i++) {
> + iowrite8(0xff, info->virt + offset);
> + offset += 2;
> + if (unlikely(offset == 0)) {
> + info->active_bank++;
> + iowrite8(info->active_bank, info->bank);
> + }
> + }
> + mutex_unlock(&info->lock);
> + instr->state = MTD_ERASE_DONE;
> + mtd_erase_callback(instr);
> +
> + return 0;
> +}
> +
> +static int
> +lp8x4x_sram_write(struct mtd_info *mtd, loff_t to, size_t len,
> + size_t *retlen, const u_char *b)
> +{
> + struct lp8x4x_sram_info *info = mtd->priv;
> + unsigned bank = to >> 11;
> + unsigned offset = (to & 0x7ff) << 1;
> + loff_t i;
> +
> + mutex_lock(&info->lock);
> + if (unlikely(bank != info->active_bank)) {
> + info->active_bank = bank;
> + iowrite8(bank, info->bank);
> + }
> + for (i = 0; i < len; i++) {
> + iowrite8(b[i], info->virt + offset);
> + offset += 2;
> + if (unlikely(offset == 0)) {
> + info->active_bank++;
> + iowrite8(info->active_bank, info->bank);
> + }
> + }
> + mutex_unlock(&info->lock);
> + *retlen = len;
> + return 0;
> +}
> +
> +static int
> +lp8x4x_sram_read(struct mtd_info *mtd, loff_t from, size_t len,
> + size_t *retlen, u_char *b)
> +{
> + struct lp8x4x_sram_info *info = mtd->priv;
> + unsigned bank = from >> 11;
> + unsigned offset = (from & 0x7ff) << 1;
> + loff_t i;
> +
> + mutex_lock(&info->lock);
> + if (unlikely(bank != info->active_bank)) {
> + info->active_bank = bank;
> + iowrite8(bank, info->bank);
> + }
> + for (i = 0; i < len; i++) {
> + b[i] = ioread8(info->virt + offset);
> + offset += 2;
> + if (unlikely(offset == 0)) {
> + info->active_bank++;
> + iowrite8(info->active_bank, info->bank);
> + }
> + }
> + mutex_unlock(&info->lock);
> + *retlen = len;
> + return 0;
> +}
> +
> +static struct of_device_id of_flash_match[] = {
> + {
> + .compatible = "icpdas,sram-lp8x4x",
> + },
> + { },
> +};
> +MODULE_DEVICE_TABLE(of, of_flash_match);
> +
> +static int
> +lp8x4x_sram_probe(struct platform_device *pdev)
> +{
> + const struct of_device_id *match;
> + struct lp8x4x_sram_info *info;
> + struct resource *res_virt, *res_bank;
> + char sz_str[16];
> + struct mtd_part_parser_data ppdata;
> + int err = 0;
> +
> + match = of_match_device(of_flash_match, &pdev->dev);
> + if (!match)
> + return -EINVAL;

Does this of_match_device() serve any particular purpose? Your driver
already matches against these IDs, and you're not actually retrieving
any of-data from the match, so this looks redundant.

> +
> + info = devm_kzalloc(&pdev->dev, sizeof(*info), GFP_KERNEL);
> + if (!info)
> + return -ENOMEM;
> +
> + res_virt = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> + info->virt = devm_ioremap_resource(&pdev->dev, res_virt);
> + if (IS_ERR(info->virt))
> + return PTR_ERR(info->virt);
> +
> + res_bank = platform_get_resource(pdev, IORESOURCE_MEM, 1);
> + info->bank = devm_ioremap_resource(&pdev->dev, res_bank);
> + if (IS_ERR(info->bank))
> + return PTR_ERR(info->bank);
> +
> + info->mtd.priv = info;
> + info->mtd.name = "SRAM";

Are you absolutely sure there is only ever a single SRAM device on a
given system? Because otherwise, you will get redundantly-named MTD's.
If the answer is no, you might consider a unique naming scheme.

> + info->mtd.type = MTD_RAM;
> + info->mtd.flags = MTD_CAP_RAM;
> + info->mtd.size = resource_size(res_virt) << 7;
> + info->mtd.erasesize = 512;
> + info->mtd.writesize = 4;
> + info->mtd._erase = lp8x4x_sram_erase;
> + info->mtd._write = lp8x4x_sram_write;
> + info->mtd._read = lp8x4x_sram_read;
> + info->mtd.owner = THIS_MODULE;
> +
> + mutex_init(&info->lock);
> + iowrite8(info->active_bank, info->bank);
> + platform_set_drvdata(pdev, info);
> +
> + ppdata.of_node = pdev->dev.of_node;
> + err = mtd_device_parse_register(&info->mtd, NULL, &ppdata,
> + NULL, 0);
> +
> + if (err < 0) {
> + dev_err(&pdev->dev, "failed to register MTD\n");
> + return err;
> + }
> +
> + string_get_size(info->mtd.size, STRING_UNITS_2, sz_str,
> + sizeof(sz_str));
> + dev_info(&pdev->dev, "using %s SRAM on LP-8X4X as %s\n", sz_str,
> + dev_name(&info->mtd.dev));
> + return 0;
> +}
> +
> +static int
> +lp8x4x_sram_remove(struct platform_device *dev)
> +{
> + struct lp8x4x_sram_info *info = platform_get_drvdata(dev);
> + return mtd_device_unregister(&info->mtd);
> +}
> +
> +static struct platform_driver lp8x4x_sram_driver = {
> + .driver = {
> + .name = "sram-lp8x4x",
> + .owner = THIS_MODULE,
> + .of_match_table = of_flash_match,
> + },
> + .probe = lp8x4x_sram_probe,
> + .remove = lp8x4x_sram_remove,
> +};
> +
> +module_platform_driver(lp8x4x_sram_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Sergei Ianovich <ynvich@gmail.com>");
> +MODULE_DESCRIPTION("MTD driver for SRAM on ICPDAS LP-8x4x");

Thanks,
Brian


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