linux-kernel - Re: [PATCH v2] spi: spi-imx: Fix spi_bus_clk if requested clock is higher than input clock

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Message-ID: <20221115165413.4tvmhiv64gdmctml@pengutronix.de>
Date:   Tue, 15 Nov 2022 17:54:13 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Frieder Schrempf <frieder@...s.de>
Cc:     David Jander <david@...tonic.nl>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>, Marek Vasut <marex@...x.de>,
        NXP Linux Team <linux-imx@....com>, stable@...r.kernel.org,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Baruch Siach <baruch.siach@...lu.com>,
        Fabio Estevam <festevam@...il.com>,
        Minghao Chi <chi.minghao@....com.cn>
Subject: Re: [PATCH v2] spi: spi-imx: Fix spi_bus_clk if requested clock is
 higher than input clock

On 15.11.2022 17:26:53, Frieder Schrempf wrote:
> From: Frieder Schrempf <frieder.schrempf@...tron.de>
> 
> In case the requested bus clock is higher than the input clock, the correct
> dividers (pre = 0, post = 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 clock set
> to 50 MHz by default and a requested SPI bus clock of 80 MHz for the SPI NOR
> flash.
> 
> With the fix applied the debug message from mx51_ecspi_clkdiv() now prints 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")

The *fres parameter was introduced in:

| Fixes: 6fd8b8503a0d ("spi: spi-imx: Fix out-of-order CS/SCLK operation at low speeds")

The exiting code:

|	if (unlikely(fspi > fin))
|		return 0;

was not sufficient any more and should be fixed.

Marc

-- 
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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