RE: [PATCH v3 4/4] mtd: spi-nor: Disable Micron flash HW protection

[Yunhui Cui]

Hi Bean,

Thanks for your suggestions very much.
Yes, the flash N25Q128A status register write enable/disable bit is disable in initial state.
But, This patch aims to clear status register bit[7](write enable/disable bit) to 0, which enables the bit.
Frankly speaking, I also don't want to add this patch.
The reason for this is that clear status register bit[7] to 0 is a must to set quad mode to Enhanced Volatile Configuration Register using command SPINOR_OP_WD_EVCR. Otherwise it will output "Micron EVCR Quad bit not clear" in spi-nor.c
I looked up the datasheet, but I really don't find out any connection between status register bit[7](write enable/disable bit) equals 0 and seting quad mode to Enhanced Volatile Configuration Register.

Just as I want to send the issue to Micron team , could you give me some solutions ?


Thanks 
Yunhui

-----Original Message-----
From: Bean Huo 霍斌斌 (beanhuo) [mailto:beanhuo@xxxxxxxxxx] 
Sent: Thursday, March 03, 2016 9:39 PM
To: Yunhui Cui
Cc: linux-mtd@xxxxxxxxxxxxxxxxxxx; dwmw2@xxxxxxxxxxxxx; computersforpeace@xxxxxxxxx; han.xu@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-mtd@xxxxxxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Yao Yuan; Yunhui Cui
Subject: Re: [PATCH v3 4/4] mtd: spi-nor: Disable Micron flash HW protection

> From: Yunhui Cui <B56489@xxxxxxxxxxxxx>
> To: <dwmw2@xxxxxxxxxxxxx>, <computersforpeace@xxxxxxxxx>,
> 	<han.xu@xxxxxxxxxxxxx>
> Cc: <linux-kernel@xxxxxxxxxxxxxxx>, <linux-mtd@xxxxxxxxxxxxxxxxxxx>,
> 	<linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, <yao.yuan@xxxxxxx>, Yunhui 
> Cui
> 	<yunhui.cui@xxxxxxx>
> Subject: [PATCH v3 4/4] mtd: spi-nor: Disable Micron flash HW
> 	protection
> Message-ID: <1456988044-37061-4-git-send-email-B56489@xxxxxxxxxxxxx>
> Content-Type: text/plain
> 
> From: Yunhui Cui <yunhui.cui@xxxxxxx>
> 
> For Micron family ,The status register write enable/disable bit, 
> provides hardware data protection for the device.
> When the enable/disable bit is set to 1, the status register 
> nonvolatile bits become read-only and the WRITE STATUS REGISTER 
> operation will not execute.
> 
> Signed-off-by: Yunhui Cui <yunhui.cui@xxxxxxx>
> ---
>  drivers/mtd/spi-nor/spi-nor.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/spi-nor.c 
> b/drivers/mtd/spi-nor/spi-nor.c index ed0c19c..917f814 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -39,6 +39,7 @@
> 
>  #define SPI_NOR_MAX_ID_LEN	6
>  #define SPI_NOR_MAX_ADDR_WIDTH	4
> +#define SPI_NOR_MICRON_WRITE_ENABLE	0x7f
> 
>  struct flash_info {
>  	char		*name;
> @@ -1238,6 +1239,14 @@ int spi_nor_scan(struct spi_nor *nor, const 
> char *name, enum read_mode mode)
>  		write_sr(nor, 0);
>  	}
> 
> +	if (JEDEC_MFR(info) == SNOR_MFR_MICRON) {
> +		ret = read_sr(nor);
> +		ret &= SPI_NOR_MICRON_WRITE_ENABLE;
> +
For Micron the status register write enable/disable bit, its default/factory value is disable.
Can here first check ,then program?
> +		write_enable(nor);
> +		write_sr(nor, ret);
> +	}
> +
>  	if (!mtd->name)
>  		mtd->name = dev_name(dev);
>  	mtd->priv = nor;