linux-kernel - Re: [PATCH v13 11/15] mtd: spi-nor: core: perform a Soft Reset on shutdown

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Message-ID: <a32450dc-8db3-597c-34b0-68632ac27184@microchip.com>
Date:   Wed, 30 Sep 2020 07:32:58 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <p.yadav@...com>, <miquel.raynal@...tlin.com>, <richard@....at>,
        <vigneshr@...com>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
CC:     <nsekhar@...com>, <boris.brezillon@...labora.com>
Subject: Re: [PATCH v13 11/15] mtd: spi-nor: core: perform a Soft Reset on
 shutdown

On 9/29/20 4:08 PM, Pratyush Yadav wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 16/09/20 06:14PM, Pratyush Yadav wrote:
>> Perform a Soft Reset on shutdown on flashes that support it so that the
>> flash can be reset to its initial state and any configurations made by
>> spi-nor (given that they're only done in volatile registers) will be
>> reset. This will hand back the flash in pristine state for any further
>> operations on it.
>>
>> Signed-off-by: Pratyush Yadav <p.yadav@...com>
>> ---
>>  drivers/mtd/spi-nor/core.c  | 41 +++++++++++++++++++++++++++++++++++++
>>  include/linux/mtd/spi-nor.h |  2 ++
>>  2 files changed, 43 insertions(+)
>>
>> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
>> index 6ee93544d72f..853dfa02f0de 100644
>> --- a/drivers/mtd/spi-nor/core.c
>> +++ b/drivers/mtd/spi-nor/core.c
>> @@ -40,6 +40,9 @@
>>
>>  #define SPI_NOR_MAX_ADDR_WIDTH       4
>>
>> +#define SPI_NOR_SRST_SLEEP_MIN 200
>> +#define SPI_NOR_SRST_SLEEP_MAX 400
>> +
>>  /**
>>   * spi_nor_get_cmd_ext() - Get the command opcode extension based on the
>>   *                      extension type.
>> @@ -3174,6 +3177,41 @@ static int spi_nor_init(struct spi_nor *nor)
>>       return 0;
>>  }
>>
>> +static void spi_nor_soft_reset(struct spi_nor *nor)
>> +{
>> +     struct spi_mem_op op;
>> +     int ret;
>> +
>> +     op = (struct spi_mem_op)SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_SRSTEN, 8),

can we avoid the cast?

> 
> The buswidth used here should be 1 instead of 8. It makes no difference
> in practice because the call to spi_nor_spimem_setup_op() immediately
> after will over-write it to the correct value anyway, but let's follow
> the style followed throughout the rest of the codebase. Will fix in the
> next version.

or you can just set the buswidth to 0 so that the reader rises his eyebrow
and search for where it is updated. If you like it better you'll have to change
throughout the entire code base, maybe in 4/15 where setup_op is introduced.

> 
>> +                     SPI_MEM_OP_NO_DUMMY,
>> +                     SPI_MEM_OP_NO_ADDR,
>> +                     SPI_MEM_OP_NO_DATA);
>> +     spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);

Still not a big fan of this, but we can update the op init later on. How
about some new lines around spi_nor_spimem_setup_op()? First time I read
the code I haven't seen it.

>> +     ret = spi_mem_exec_op(nor->spimem, &op);
>> +     if (ret) {
>> +             dev_warn(nor->dev, "Software reset failed: %d\n", ret);
>> +             return;
>> +     }
>> +
>> +     op = (struct spi_mem_op)SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_SRST, 8),
> 
> Same here.
> 
>> +                     SPI_MEM_OP_NO_DUMMY,
>> +                     SPI_MEM_OP_NO_ADDR,
>> +                     SPI_MEM_OP_NO_DATA);
>> +     spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
>> +     ret = spi_mem_exec_op(nor->spimem, &op);
>> +     if (ret) {
>> +             dev_warn(nor->dev, "Software reset failed: %d\n", ret);
>> +             return;
>> +     }
>> +
>> +     /*
>> +      * Software Reset is not instant, and the delay varies from flash to
>> +      * flash. Looking at a few flashes, most range somewhere below 100
>> +      * microseconds. So, sleep for a range of 200-400 us.
>> +      */
>> +     usleep_range(SPI_NOR_SRST_SLEEP_MIN, SPI_NOR_SRST_SLEEP_MAX);
>> +}
>> +
>>  /* mtd resume handler */
>>  static void spi_nor_resume(struct mtd_info *mtd)
>>  {
> 
> --
> Regards,
> Pratyush Yadav
> Texas Instruments India
>