Re: [PATCH v7 01/34] i2c: tegra: Make tegra_i2c_flush_fifos() usable in atomic transfer

Dmitry Osipenko
2020-09-17T19:55:30Z

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@rere.qmqm.pl>
>> Signed-off-by: Dmitry Osipenko <digetx@gmail.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.