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

Thierry Reding
2020-09-17T11:14:45Z

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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.

> + 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".

Thierry

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