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

From: Pratyush Yadav <p.yadav@ti.com>
To: <Tudor.Ambarus@microchip.com>
Cc: vigneshr@ti.com, richard@nod.at, nsekhar@ti.com,
	linux-kernel@vger.kernel.org, boris.brezillon@collabora.com,
	linux-mtd@lists.infradead.org, miquel.raynal@bootlin.com
Subject: Re: [PATCH v13 11/15] mtd: spi-nor: core: perform a Soft Reset on shutdown
Date: Wed, 30 Sep 2020 13:13:09 +0530	[thread overview]
Message-ID: <20200930074307.rdi6352fy3is6gjq@ti.com> (raw)
In-Reply-To: <a32450dc-8db3-597c-34b0-68632ac27184@microchip.com>

On 30/09/20 07:32AM, Tudor.Ambarus@microchip.com wrote:
> 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@ti.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?

No. The compiler complains about "expected expression before '{' token". 
We can avoid it if the assignment is with the declaration but then we 
can't re-use the variable op for the second command.

I like the cast better than using separate variables for the two (or 
more in other cases) commands we execute.

> > 
> > 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.

Ok. Will change it.

> > 
> >> +                     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.

Ok.

> >> +     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

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