linux-kernel - Re: [PATCH v7 01/34] i2c: tegra: Make tegra_i2c_flush

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Date:   Thu, 17 Sep 2020 17:57:15 +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 01/34] i2c: tegra: Make tegra_i2c_flush_fifos() usable
 in atomic transfer

17.09.2020 14:10, Thierry Reding пишет:
> On Wed, Sep 09, 2020 at 01:39:33AM +0300, Dmitry Osipenko wrote:
>> The tegra_i2c_flush_fifos() shouldn't sleep in atomic transfer and jiffies
>> are not updating if interrupts are disabled. Let's switch to use iopoll
>> API helpers for register-polling. The iopoll API provides helpers for both
>> atomic and non-atomic cases.
>>
>> Note that this patch doesn't fix any known problem because normally FIFO
>> is flushed at the time of starting a new transfer.
>>
>> Reviewed-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/i2c/busses/i2c-tegra.c | 25 ++++++++++++++++---------
>>  1 file changed, 16 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>> index 00d3e4d7a01e..ab88cdd70376 100644
>> --- a/drivers/i2c/busses/i2c-tegra.c
>> +++ b/drivers/i2c/busses/i2c-tegra.c
>> @@ -470,9 +470,9 @@ static int tegra_i2c_init_dma(struct tegra_i2c_dev *i2c_dev)
>>  
>>  static int tegra_i2c_flush_fifos(struct tegra_i2c_dev *i2c_dev)
>>  {
>> -	unsigned long timeout = jiffies + HZ;
>> -	unsigned int offset;
>> -	u32 mask, val;
>> +	u32 mask, val, offset, reg_offset;
> 
> Is there are reason why we need reg_offset? Seems to me like we could
> simplify this, see below.

The reason is that this patch addresses potential problem, hence it's
not a cleanup change and it should be kept minimal.

>> +	void __iomem *addr;
>> +	int err;
>>  
>>  	if (i2c_dev->hw->has_mst_fifo) {
>>  		mask = I2C_MST_FIFO_CONTROL_TX_FLUSH |
>> @@ -488,12 +488,19 @@ static int tegra_i2c_flush_fifos(struct tegra_i2c_dev *i2c_dev)
>>  	val |= mask;
>>  	i2c_writel(i2c_dev, val, offset);
>>  
>> -	while (i2c_readl(i2c_dev, offset) & mask) {
>> -		if (time_after(jiffies, timeout)) {
>> -			dev_warn(i2c_dev->dev, "timeout waiting for fifo flush\n");
>> -			return -ETIMEDOUT;
>> -		}
>> -		usleep_range(1000, 2000);
>> +	reg_offset = tegra_i2c_reg_addr(i2c_dev, offset);
>> +	addr = i2c_dev->base + reg_offset;
> 
> Why not just:
> 
> 	offset = tegra_i2c_reg_offset(i2c_dev, offset);
> 	addr = i2c_dev->base + offset;
> 
> or even just:
> 
> 	addr = i2c_dev->base + tegra_i2c_reg_offset(i2c_dev, offset);
> 
> ? That makes the patch much smaller because you don't have to rewrite
> the whole variable declaration block and just add the "addr" and "err"
> variables while removing "timeout".

There is a further "cleanup" patch named "Factor out register polling
into separate function" that already implements yours suggestion.