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Subject: Re: [PATCH 1/2] mtd: spi-nor: create/Export parameter softwareseq for
 intel-spi driver to user
To:     Daniel Walker <danielwa@cisco.com>,
        Andrew Morton <akpm@linux-foundation.org>
CC:     Bobby Liu <bobbliu@cisco.com>, <xe-linux-external@cisco.com>,
        Tudor Ambarus <tudor.ambarus@microchip.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>
References: <20200518175930.10948-1-danielwa@cisco.com>
From:   Vignesh Raghavendra <vigneshr@ti.com>
Message-ID: <589a2ef5-e086-766d-44b3-1d2b990f1f67@ti.com>
Date:   Thu, 28 May 2020 16:16:38 +0530
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+Mika Westerberg original author of the driver

On 18/05/20 11:29 pm, Daniel Walker wrote:
> From: Bobby Liu <bobbliu@cisco.com>
> 
> How to use:
> append softwareseq=1 while probe the driver.
> example:
> modprobe intel-spi writeable=1 softwareseq=1
> it will let driver use software sequence to write register for opt=EN4B
> by default it's 0 if not specified, driver will do usual HW cycle
> 

Could some one from Intel please review this patch?

Regards
Vignesh

> Why this parameter is posted to user:
> Intel PCH provides two groups of registers for SPI flash operation,
> Hard Sequence registers and Software Sequence registers,
> corresponding to intel_spi_hw_cycle() and intel_spi_sw_cycle()
> respectively in driver code. But HW sequence register won't send EN4B
> opcode to SPI flash. BIOS code use SW register to send EN4B.
> 
> On some Cisco routers, two 32M SPI flashes, which require 4-byte address mode enabled,
> are physically connected to an FPGA, one flash is active and one is inactive.
> When we do BIOS upgrade, we need switch to the inactive one,
> but unfortunately, this one is still 3-byte address mode as default,
> after we do real-time switch, we need reload SPI driver to send EN4B code to
> enable 4-byte address mode.
> 
> Refering to our BIOS code, Software sequence register is processed
> while sending EN4B opcode. So here we use sw_cycle in driver for EN4B as well.
> 
> Why I don't just easily use software sequence for all:
> 1.It will impact all flash operation, include flash W/R, high risk
> 2.The only SPI type I can use is INTEL_SPI_BXT according to datasheet,
>   this will require using hw seq.
>   I tried to specify other SPI type, it couldn't work with Intel PCH.
>   If I force SW seq for all, during boot up, sw_cycle fails to read
>   vendor ID.
> 
> In conclusion, I only use SW cycle for EN4B opcode to minimize impact.
> It won't impact other users as well.
> 
> Why the default flash can work at 4-byte address mode:
> BIOS sets 4-byte address mode for the current active SPI flash with SW seq registers.
> So we don't need append softwareseq=1 for normal boot up script,
> it will only be used in BIOS upgrade script.
> 
> Cc: xe-linux-external@cisco.com
> Signed-off-by: Bobby Liu <bobbliu@cisco.com>
> [ danielwa: edited the commit message a little. ]
> Signed-off-by: Daniel Walker <danielwa@cisco.com>
> ---
>  drivers/mtd/spi-nor/controllers/intel-spi.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/controllers/intel-spi.c b/drivers/mtd/spi-nor/controllers/intel-spi.c
> index 61d2a0ad2131..e5a3d51a2e4d 100644
> --- a/drivers/mtd/spi-nor/controllers/intel-spi.c
> +++ b/drivers/mtd/spi-nor/controllers/intel-spi.c
> @@ -163,6 +163,10 @@ static bool writeable;
>  module_param(writeable, bool, 0);
>  MODULE_PARM_DESC(writeable, "Enable write access to SPI flash chip (default=0)");
>  
> +static bool softwareseq;
> +module_param(softwareseq, bool, 0);
> +MODULE_PARM_DESC(softwareseq, "Use software sequence for register write (default=0)");
> +
>  static void intel_spi_dump_regs(struct intel_spi *ispi)
>  {
>  	u32 value;
> @@ -619,6 +623,18 @@ static int intel_spi_write_reg(struct spi_nor *nor, u8 opcode, const u8 *buf,
>  	if (ret)
>  		return ret;
>  
> +	/*
> +	 * Intel Skylake will not send EN4B to SPI flash if we use HW sequence
> +	 * Here export one interface "softwareseq" to OS,
> +	 * let driver user decide if use SW sequence or not
> +	 */
> +	if (opcode == SPINOR_OP_EN4B && softwareseq) {
> +	    dev_info(ispi->dev,
> +		"Write register opcode is SPINOR_OP_EN4B, do SW cycle\n");
> +	    return intel_spi_sw_cycle(ispi, opcode, len,
> +		OPTYPE_WRITE_NO_ADDR);
> +	}
> +
>  	if (ispi->swseq_reg)
>  		return intel_spi_sw_cycle(ispi, opcode, len,
>  					  OPTYPE_WRITE_NO_ADDR);
>