linux-kernel - Re: [PATCH v7 06/34] i2c: tegra: Remove i2c_dev.clk_divisor_non_hs

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Date:   Thu, 17 Sep 2020 18:27:28 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 06/34] i2c: tegra: Remove
 i2c_dev.clk_divisor_non_hs_mode member

17.09.2020 14:25, Thierry Reding пишет:
> On Wed, Sep 09, 2020 at 01:39:38AM +0300, Dmitry Osipenko wrote:
>> The "non_hs_mode" divisor value is fixed, thus there is no need to have
>> the variable i2c_dev.clk_divisor_non_hs_mode struct member. Let's remove
>> it and move the mode selection into tegra_i2c_init() where it can be
>> united with the timing selection.
>>
>> Reviewed-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/i2c/busses/i2c-tegra.c | 46 ++++++++++++++++------------------
>>  1 file changed, 21 insertions(+), 25 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>> index 720a75439e91..85ed0e02d48c 100644
>> --- a/drivers/i2c/busses/i2c-tegra.c
>> +++ b/drivers/i2c/busses/i2c-tegra.c
>> @@ -250,7 +250,6 @@ struct tegra_i2c_hw_feature {
>>   * @msg_buf_remaining: size of unsent data in the message buffer
>>   * @msg_read: identifies read transfers
>>   * @bus_clk_rate: current I2C bus clock rate
>> - * @clk_divisor_non_hs_mode: clock divider for non-high-speed modes
>>   * @is_multimaster_mode: track if I2C controller is in multi-master mode
>>   * @tx_dma_chan: DMA transmit channel
>>   * @rx_dma_chan: DMA receive channel
>> @@ -281,7 +280,6 @@ struct tegra_i2c_dev {
>>  	size_t msg_buf_remaining;
>>  	int msg_read;
>>  	u32 bus_clk_rate;
>> -	u16 clk_divisor_non_hs_mode;
>>  	bool is_multimaster_mode;
>>  	struct dma_chan *tx_dma_chan;
>>  	struct dma_chan *rx_dma_chan;
>> @@ -783,6 +781,7 @@ static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
>>  	u32 val;
>>  	int err;
>>  	u32 clk_divisor, clk_multiplier;
>> +	u32 non_hs_mode;
>>  	u32 tsu_thd;
>>  	u8 tlow, thigh;
>>  
>> @@ -805,24 +804,33 @@ static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
>>  	if (i2c_dev->is_vi)
>>  		tegra_i2c_vi_init(i2c_dev);
>>  
>> -	/* Make sure clock divisor programmed correctly */
>> -	clk_divisor = FIELD_PREP(I2C_CLK_DIVISOR_HSMODE,
>> -				 i2c_dev->hw->clk_divisor_hs_mode) |
>> -		      FIELD_PREP(I2C_CLK_DIVISOR_STD_FAST_MODE,
>> -				 i2c_dev->clk_divisor_non_hs_mode);
>> -	i2c_writel(i2c_dev, clk_divisor, I2C_CLK_DIVISOR);
>> -
>> -	if (i2c_dev->bus_clk_rate > I2C_MAX_STANDARD_MODE_FREQ &&
>> -	    i2c_dev->bus_clk_rate <= I2C_MAX_FAST_MODE_PLUS_FREQ) {
>> +	switch (i2c_dev->bus_clk_rate) {
>> +	case I2C_MAX_STANDARD_MODE_FREQ + 1 ... I2C_MAX_FAST_MODE_PLUS_FREQ:
> 
> Is there are particular reason for switching the simple conditional to a
> switch here? The old variant looks much easier to understand to me.

The reason is make it readable :) For me it's too difficult to read > <=
&& { } + no proper indentation.

The switches are more suitable for ranges, IMO. Especially when there
are multiple ranges, and there could be more ranges in the future in
this code.