linux-kernel - Re: [PATCH v3] spi: spi-imx: Fix spi_bus_clk if requested clock is higher than input clock

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Message-ID: <c0aeb578-611b-d008-cdc6-148f99bf19c2@denx.de>
Date:   Wed, 16 Nov 2022 11:49:33 +0100
From:   Marek Vasut <marex@...x.de>
To:     Frieder Schrempf <frieder.schrempf@...tron.de>,
        Frieder Schrempf <frieder@...s.de>,
        David Jander <david@...tonic.nl>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org, Marc Kleine-Budde <mkl@...gutronix.de>,
        Mark Brown <broonie@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>
Cc:     Fabio Estevam <festevam@...il.com>, stable@...r.kernel.org,
        Baruch Siach <baruch.siach@...lu.com>,
        Minghao Chi <chi.minghao@....com.cn>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [PATCH v3] spi: spi-imx: Fix spi_bus_clk if requested clock is
 higher than input clock

On 11/16/22 09:17, Frieder Schrempf wrote:
> On 16.11.22 00:49, Marek Vasut wrote:
>> On 11/15/22 19:10, 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: 6fd8b8503a0d ("spi: spi-imx: Fix out-of-order CS/SCLK operation
>>> at low speeds")
>>> Fixes: 07e759387788 ("spi: spi-imx: add PIO polling support")
>>> Cc: Marc Kleine-Budde <mkl@...gutronix.de>
>>> Cc: David Jander <david@...tonic.nl>
>>> Cc: Fabio Estevam <festevam@...il.com>
>>> Cc: Mark Brown <broonie@...nel.org>
>>> Cc: Marek Vasut <marex@...x.de>
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
>>> Tested-by: Fabio Estevam <festevam@...il.com>
>>> ---
>>>
>>> Changes for v3:
>>>
>>> * Add back the Fixes tag for commit 6fd8b8503a0d
>>> * Add Fabio's Tested-by (Thanks!)
>>>
>>> Changes for v2:
>>>
>>> * Remove the reference and the Fixes tag for commit 6fd8b8503a0d as it is
>>>     incorrect.
>>> ---
>>>    drivers/spi/spi-imx.c | 3 +--
>>>    1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
>>> index 30d82cc7300b..468ce0a2b282 100644
>>> --- a/drivers/spi/spi-imx.c
>>> +++ b/drivers/spi/spi-imx.c
>>> @@ -444,8 +444,7 @@ static unsigned int mx51_ecspi_clkdiv(struct
>>> spi_imx_data *spi_imx,
>>>        unsigned int pre, post;
>>>        unsigned int fin = spi_imx->spi_clk;
>>>    -    if (unlikely(fspi > fin))
>>> -        return 0;
>>> +    fspi = min(fspi, fin);
>>>          post = fls(fin) - fls(fspi);
>>>        if (fin > fspi << post)
>>
>> Can you also test the SPI flash at some 100 kHz, just to see whether it
>> still works properly ? (to retain behavior fixed first in 6fd8b8503a0dc
>> ("spi: spi-imx: Fix out-of-order CS/SCLK operation at low speeds") )
>>
>> The fix here does look fine by me however.
> 
> I successfully tested at 100 kHZ SPI bus clock. As in this case fspi is
> lower than fin, the patch doesn't change anything in the code path and
> therefore the behavior introduced in 6fd8b8503a0dc stays the same as
> without the patch.

Acked-by: Marek Vasut <marex@...x.de>

Thanks for the extra check !