linux-kernel - Re: [PATCH v2 4/8] mtd: spi-nor: core: Introduce method for RDID op

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Message-ID: <eca7100c7e6dacd9cb9e18b5bee3e2ab@walle.cc>
Date:   Tue, 22 Mar 2022 09:19:49 +0100
From:   Michael Walle <michael@...le.cc>
To:     Pratyush Yadav <p.yadav@...com>
Cc:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        miquel.raynal@...tlin.com, richard@....at, vigneshr@...com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        nicolas.ferre@...rochip.com
Subject: Re: [PATCH v2 4/8] mtd: spi-nor: core: Introduce method for RDID op

Am 2022-03-22 08:32, schrieb Pratyush Yadav:
> On 21/03/22 11:56PM, Michael Walle wrote:
>> Am 2022-02-28 12:17, schrieb Tudor Ambarus:
>> > RDID is used in the core to auto detect the flash, but also by some
>> > manufacturer drivers that contain flashes that support Octal DTR mode,
>> > so that they can read the flash ID after the switch to Octal DTR was
>> > made
>> > to test if the switch was successful. Introduce a core method for RDID
>> > op
>> > to avoid code duplication.
>> 
>> Some or all? Is that specific to the flash or can we just check that
>> readid works in spi_nor_octal_dtr_enable()? That way we could also
>> just get rid of the proto parameter for the read_id because it can
>> be called after we set the reg_proto.
> 
> It is specific to the flash. Not all flashes support RDID in 8D mode.
> And the RDID command is also different in 8D mode for various flashes.
> For example, Micron MT35XU512ABA flash expects 8 dummy cycles and 0
> address cycles. Cypress S28HS512T expects 4 address cycles and 3 dummy
> cycles.
> 
> The octal_dtr_enable hook would know what parameters to use but it is
> harder for the core to know since this information is not discoverable
> via SFDP.

Ah, I see, thanks for clarification.

-michael