linux-kernel - Re: [PATCH 3/4] mtd: rawnand: gpmi: validate controller clock rate

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Message-Id: <20220123153941.673301-1-miquel.raynal@bootlin.com>
Date:   Sun, 23 Jan 2022 16:39:41 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>,
        linux-kernel@...r.kernel.org
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        Sascha Hauer <s.hauer@...gutronix.de>, Han Xu <han.xu@....com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd@...ts.infradead.org
Subject: Re: [PATCH 3/4] mtd: rawnand: gpmi: validate controller clock rate

On Tue, 2022-01-18 at 09:54:33 UTC, Dario Binacchi wrote:
> What to do when the real rate of the gpmi clock is not equal to the
> required one? The solutions proposed in [1] did not lead to a conclusion
> on how to validate the clock rate, so, inspired by the document [2], I
> consider the rate correct only if not lower or equal to the rate of the
> previous edo mode. In fact, in chapter 4.16.2 (NV-DDR) of the document [2],
> it is written that "If the host selects timing mode n, then its clock
> period shall be faster than the clock period of timing mode n-1 and
> slower than or equal to the clock period of timing mode n.". I thought
> that it could therefore also be used in this case, without therefore
> having to define the valid rate ranges empirically.
> 
> For example, suppose that gpmi_nfc_compute_timings() is called to set
> edo mode 5 (100MHz) but the rate returned by clk_round_rate() is 80MHz
> (edo mode 4). In this case gpmi_nfc_compute_timings() will return error,
> and will be called again to set edo mode 4, which this time will be
> successful.
> 
> [1] https://lore.kernel.org/r/20210702065350.209646-5-ebiggers@kernel.org
> [2] http://www.onfi.org/-/media/client/onfi/specs/onfi_3_0_gold.pdf?la=en
> 
> Co-developed-by: Michael Trimarchi <michael@...rulasolutions.com>
> Signed-off-by: Michael Trimarchi <michael@...rulasolutions.com>
> Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> Tested-by: Sascha Hauer <s.hauer@...gutronix.de>
> Reviewed-by: Sascha Hauer <s.hauer@...gutronix.de>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git nand/next, thanks.

Miquel