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Subject: Re: [RFC PATCH 1/5] mtd: cfi_cmdset_0002: Add support for polling
 status register
To:     "Vignesh R (by way of Boris Brezillon <bbrezillon@kernel.org>)" 
        <vigneshr@ti.com>, David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Boris Brezillon <bbrezillon@kernel.org>,
        Marek Vasut <marek.vasut@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Rob Herring <robh+dt@kernel.org>
Cc:     devicetree@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
        tudor.ambarus@microchip.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        nsekhar@ti.com, linux-kernel@vger.kernel.org,
        linux-mtd@lists.infradead.org, linux-arm-kernel@lists.infradead.org
References: <20190219063607.29949-1-vigneshr@ti.com>
 <20190219063607.29949-2-vigneshr@ti.com>
From:   Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Organization: Cogent Embedded
Message-ID: <4fb5aac2-d421-c7df-ab1c-9a9290f068e3@cogentembedded.com>
Date:   Sat, 23 Feb 2019 21:41:06 +0300
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Hello!

On 02/19/2019 09:36 AM, Vignesh R (by way of Boris Brezillon <bbrezillon@kernel.org>) wrote:

> HyperFlash devices are compliant with CFI AMD/Fujitsu Extended Command
> Set(0x0002) for flash operations, therefore drivers/mtd/chips/cfi_cmdset_0002.c
> can be use as is. But these devices do not support DQ polling method of
> determining chip ready/good status. These flashes provide Status
> Register whose bits can be polled to know status of flash operation.
> 
> Cypress HyperFlash datasheet here[1], talks about CFI Amd/Fujitsu
> Extended Query version 1.5. Bit 0 of "Software Features supported" field
> of CFI Primary Vendor-Specific Extended Query table indicates
> presence/absence of status register and Bit 1 indicates whether or not
> DQ polling is supported. Using these bits, its possible to determine
> whether flash supports DQ polling or need to use Status Register.
> 
> Add support for polling status register to know device ready/status of
> erase/write operations when DQ polling is not supported.
> 
> [1] https://www.cypress.com/file/213346/download
> 
> Signed-off-by: Vignesh R <vigneshr@ti.com>
> ---
> 
> Note: PRI extended query table size is bigger on 1.5 than on older
> revision. Not sure if this causes problems on older rev. because of
> reading beyond current size.
> 
>  drivers/mtd/chips/cfi_cmdset_0002.c | 50 +++++++++++++++++++++++++++++
>  include/linux/mtd/cfi.h             |  5 +++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c b/drivers/mtd/chips/cfi_cmdset_0002.c
> index 72428b6bfc47..7a4ef0237750 100644
> --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
[...]
> @@ -97,6 +105,18 @@ static struct mtd_chip_driver cfi_amdstd_chipdrv = {
>  	.module		= THIS_MODULE
>  };
>  
> +/*
> + * Use status register to poll for Erase/write completion when DQ is not
> + * supported. This is indicated by Bit[1:0] of SoftwareFeatures field in
> + * CFI Primary Vendor-Specific Extended Query table 1.5
> + */
> +static int cfi_use_status_reg(struct cfi_private *cfi)
> +{
> +	struct cfi_pri_amdstd *extp = cfi->cmdset_priv;
> +
> +	return (extp->MinorVersion >= '5') &&
> +		((extp->SoftwareFeatures & 0x11) == 1);

   Parens not necessary here.

[...]
> @@ -744,8 +764,21 @@ static struct mtd_info *cfi_amdstd_setup(struct mtd_info *mtd)
>   */
>  static int __xipram chip_ready(struct map_info *map, unsigned long addr)
>  {
> +	struct cfi_private *cfi = map->fldrv_priv;
>  	map_word d, t;
>  
> +	if (cfi_use_status_reg(cfi)) {
> +		/*
> +		 * For chips that support status register, check device
> +		 * ready bit
> +		 */
> +		cfi_send_gen_cmd(0x70, cfi->addr_unlock1, 0, map, cfi,
> +				 cfi->device_type, NULL);
> +		d = map_read(map, addr);
> +
> +		return (d.x[0] & CFI_SR_DRB);

   Again, parens not needed.

[...]

   Other than that, looks good.

MBR, Sergei