linux-kernel - Re: [PATCH v3 6/9] mtd: spi-nor: core: Add helpers to read/write any register

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Message-ID: <89083a31-b862-de50-fdca-d427fb908a08@microchip.com>
Date:   Tue, 19 Apr 2022 12:56:24 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <michael@...le.cc>, <p.yadav@...com>
CC:     <miquel.raynal@...tlin.com>, <richard@....at>, <vigneshr@...com>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <Nicolas.Ferre@...rochip.com>, <Takahiro.Kuwano@...ineon.com>
Subject: Re: [PATCH v3 6/9] mtd: spi-nor: core: Add helpers to read/write any
 register

On 4/19/22 15:46, Michael Walle wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Am 2022-04-19 14:32, schrieb Pratyush Yadav:
>> On 19/04/22 12:08PM, Tudor.Ambarus@...rochip.com wrote:
>>> On 4/19/22 14:46, Michael Walle wrote:
>>> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>> >
>>> > Am 2022-04-19 13:19, schrieb Michael Walle:
>>> >> Am 2022-04-11 11:10, schrieb Tudor Ambarus:
>>> >>> There are manufacturers that use registers indexed by address. Some of
>>> >>> them support "read/write any register" opcodes. Provide core methods
>>> >>> that
>>> >>> can be used by all manufacturers. SPI NOR controller ops are
>>> >>> intentionally
>>> >>> not supported as we intend to move all the SPI NOR controller drivers
>>> >>> under the SPI subsystem.
>>> >>>
>>> >>> Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
>>> >>> Tested-by: Takahiro Kuwano <Takahiro.Kuwano@...ineon.com>
>>> >>> Reviewed-by: Pratyush Yadav <p.yadav@...com>
>>> >>
>>> >> I still don't like it because the function doesn't do
>>> >> anything what the function name might suggest. The read
>>> >> just executes an op, the write executes an op with a
>>> >> write enable before. All the behavior is determined by the
>>> >> 'op' argument.
>>> >>
>>> >> Anyway,
>>> >> Reviewed-by: Michael Walle <michael@...le.cc>
>>> >>
>>> >>> ---
>>> >>> v3: no changes
>>> >>>
>>> >>>  drivers/mtd/spi-nor/core.c | 41
>>> >>> ++++++++++++++++++++++++++++++++++++++
>>> >>>  drivers/mtd/spi-nor/core.h |  4 ++++
>>> >>>  2 files changed, 45 insertions(+)
>>> >>>
>>> >>> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
>>> >>> index 6165dc7bfd17..42794328d3b6 100644
>>> >>> --- a/drivers/mtd/spi-nor/core.c
>>> >>> +++ b/drivers/mtd/spi-nor/core.c
>>> >>> @@ -307,6 +307,47 @@ ssize_t spi_nor_write_data(struct spi_nor *nor,
>>> >>> loff_t to, size_t len,
>>> >>>      return nor->controller_ops->write(nor, to, len, buf);
>>> >>>  }
>>> >>>
>>> >>> +/**
>>> >>> + * spi_nor_read_reg() - read register to flash memory
>>> >>> + * @nor:        pointer to 'struct spi_nor'.
>>> >>> + * @op:             SPI memory operation. op->data.buf must be DMA-able.
>>> >>> + * @proto:  SPI protocol to use for the register operation.
>>> >>> + *
>>> >>> + * Return: zero on success, -errno otherwise
>>> >>> + */
>>> >>> +int spi_nor_read_reg(struct spi_nor *nor, struct spi_mem_op *op,
>>> >>> +                 enum spi_nor_protocol proto)
>>> >>> +{
>>> >>> +    if (!nor->spimem)
>>> >>> +            return -EOPNOTSUPP;
>>> >>> +
>>> >>> +    spi_nor_spimem_setup_op(nor, op, proto);
>>> >>> +    return spi_nor_spimem_exec_op(nor, op);
>>> >>> +}
>>> >>> +
>>> >>> +/**
>>> >>> + * spi_nor_write_reg() - write register to flash memory
>>> >>> + * @nor:        pointer to 'struct spi_nor'
>>> >>> + * @op:             SPI memory operation. op->data.buf must be DMA-able.
>>> >>> + * @proto:  SPI protocol to use for the register operation.
>>> >>> + *
>>> >>> + * Return: zero on success, -errno otherwise
>>> >>> + */
>>> >>> +int spi_nor_write_reg(struct spi_nor *nor, struct spi_mem_op *op,
>>> >>> +                  enum spi_nor_protocol proto)
>>> >>> +{
>>> >>> +    int ret;
>>> >>> +
>>> >>> +    if (!nor->spimem)
>>> >>> +            return -EOPNOTSUPP;
>>> >>> +
>>> >>> +    ret = spi_nor_write_enable(nor);
>>> >>> +    if (ret)
>>> >>> +            return ret;
>>> >>> +    spi_nor_spimem_setup_op(nor, op, proto);
>>> >>> +    return spi_nor_spimem_exec_op(nor, op);
>>> >
>>> > After seeing your next two patches. Shouldn't the
>>> > spi_nor_wait_until_ready() call be here too?
>>> >
>>>
>>> I thought of this too, but seems that for a reason that I don't
>>> remember, we don't call for spi_nor_wait_until_ready after we
>>> write the octal DTR bit. Pratyush, do you remember why?
>>
>> We are not sure the protocol changed correctly so we can't rely on
>> spi_nor_wait_until_ready(). We read the ID instead to be sure.
> 
> So besides the fact that the write_reg only works with the 'correct'
> op parameter, it is also tailored to the special use case. For real
> write_reg(), the user would actually has to poll the status bit
> afterwards? :(
> 
Don't be sad :D. Are the octal DTR methods an exception?
If yes, let's add the call to spi_nor_wait_until_ready() in the
read/write_any_reg() methods, and let the octal methods handle
the specific write themselves, without calling for ready()

Cheers,
ta