linux-kernel - Re: [PATCH v2 7/9] spi: spi-s3c64xx: Ensure cur

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Message-ID: <dleftj5z98xjxs.fsf%l.stelmach@samsung.com>
Date:   Mon, 24 Aug 2020 15:17:03 +0200
From:   Lukasz Stelmach <l.stelmach@...sung.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Kukjin Kim <kgene@...nel.org>, Andi Shyti <andi@...zian.org>,
        Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        m.szyprowski@...sung.com, b.zolnierkie@...sung.com,
        Tomasz Figa <tfiga@...omium.org>
Subject: Re: [PATCH v2 7/9] spi: spi-s3c64xx: Ensure cur_speed holds actual
 clock value

It was <2020-08-22 sob 14:43>, when Krzysztof Kozlowski wrote:
> On Fri, Aug 21, 2020 at 06:13:59PM +0200, Łukasz Stelmach wrote:
>> cur_speed is used to calculate transfer timeout and needs to be
>> set to the actual value of (half) the clock speed for precise
>> calculations.
>
> If you need this only for timeout calculation just divide it in
> s3c64xx_wait_for_dma().

I divide it here to keep the relationship between the value the variable
holds and the one that is inside clk_* (See? It's multiplied 3 lines
above). If you look around every single clk_get_rate() call in the file is
divided by two.

> Otherwise why only if (cmu) case is updated?

You are righ I will update that too.

However, I wonder if it is even possible that the value read from
S3C64XX_SPI_CLK_CFG would be different than the one written to it?

> You are also affecting here not only timeout but
> s3c64xx_enable_datapath() which is not mentioned in commit log. In other
> words, this looks wrong.

Indeed, there is a reference too. I've corrected the message.

>> 
>> Cc: Tomasz Figa <tfiga@...omium.org>
>> Signed-off-by: Łukasz Stelmach <l.stelmach@...sung.com>
>> ---
>>  drivers/spi/spi-s3c64xx.c | 1 +
>>  1 file changed, 1 insertion(+)
>> 
>> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
>> index 02de734b8ab1..89c162efe355 100644
>> --- a/drivers/spi/spi-s3c64xx.c
>> +++ b/drivers/spi/spi-s3c64xx.c
>> @@ -626,6 +626,7 @@ static int s3c64xx_spi_config(struct s3c64xx_spi_driver_data *sdd)
>>  		ret = clk_set_rate(sdd->src_clk, sdd->cur_speed * 2);
>>  		if (ret)
>>  			return ret;
>> +		sdd->cur_speed = clk_get_rate(sdd->src_clk) / 2;
>>  	} else {
>>  		/* Configure Clock */
>>  		val = readl(regs + S3C64XX_SPI_CLK_CFG);
>> -- 
>> 2.26.2
>> 
>
>

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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