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Date:   Tue, 15 Nov 2022 18:58:21 +0100
From:   Marc Kleine-Budde <mkl@pengutronix.de>
To:     Frieder Schrempf <frieder.schrempf@kontron.de>
Cc:     Frieder Schrempf <frieder@fris.de>,
        David Jander <david@protonic.nl>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-spi@vger.kernel.org, Mark Brown <broonie@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>, Marek Vasut <marex@denx.de>,
        NXP Linux Team <linux-imx@nxp.com>, stable@vger.kernel.org,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Baruch Siach <baruch.siach@siklu.com>,
        Fabio Estevam <festevam@gmail.com>,
        Minghao Chi <chi.minghao@zte.com.cn>
Subject: Re: [PATCH v2] spi: spi-imx: Fix spi_bus_clk if requested clock is
 higher than input clock
Message-ID: <20221115175821.4hs7k35fkxwkvew4@pengutronix.de>
References: <20221115162654.2016820-1-frieder@fris.de>
 <20221115165413.4tvmhiv64gdmctml@pengutronix.de>
 <06f8339c-4be1-159f-9374-ef8e6031da1e@kontron.de>
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On 15.11.2022 18:14:38, Frieder Schrempf wrote:
> On 15.11.22 17:54, Marc Kleine-Budde wrote:
> > On 15.11.2022 17:26:53, Frieder Schrempf wrote:
> >> From: Frieder Schrempf <frieder.schrempf@kontron.de>
> >>
> >> In case the requested bus clock is higher than the input clock, the co=
rrect
> >> dividers (pre =3D 0, post =3D 0) are returned from mx51_ecspi_clkdiv()=
, but
> >> *fres is left uninitialized and therefore contains an arbitrary value.
> >>
> >> This causes trouble for the recently introduced PIO polling feature as=
 the
> >> value in spi_imx->spi_bus_clk is used there to calculate for which
> >> transfers to enable PIO polling.
> >>
> >> Fix this by setting *fres even if no clock dividers are in use.
> >>
> >> This issue was observed on Kontron BL i.MX8MM with an SPI peripheral c=
lock set
> >> to 50 MHz by default and a requested SPI bus clock of 80 MHz for the S=
PI NOR
> >> flash.
> >>
> >> With the fix applied the debug message from mx51_ecspi_clkdiv() now pr=
ints the
> >> following:
> >>
> >> spi_imx 30820000.spi: mx51_ecspi_clkdiv: fin: 50000000, fspi: 50000000,
> >> post: 0, pre: 0
> >>
> >> Fixes: 07e759387788 ("spi: spi-imx: add PIO polling support")
>=20
> You want me to remove this tag?
>=20
> > The *fres parameter was introduced in:
> >=20
> > | Fixes: 6fd8b8503a0d ("spi: spi-imx: Fix out-of-order CS/SCLK operatio=
n at low speeds")
>=20
> and instead add back this tag? I wasn't really sure about that.

Keep both.

> >=20
> > The exiting code:
> >=20
> > |	if (unlikely(fspi > fin))
> > |		return 0;
> >=20
> > was not sufficient any more and should be fixed.
>=20
> You want me to add this in the description? Or is this just the
> explanation for why 6fd8b8503a0d should be in the Fixes tag?

No need to add the explanation to the patch.

Marc

--=20
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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