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Message-ID: <20250930012702-GYA1357001@gentoo.org>
Date: Tue, 30 Sep 2025 09:27:02 +0800
From: Yixun Lan <dlan@...too.org>
To: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
Cc: Andi Shyti <andi.shyti@...nel.org>, Alex Elder <elder@...cstar.com>,
Troy Mitchell <troymitchell988@...il.com>,
linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev
Subject: Re: [PATCH v3] i2c: spacemit: introduce pio for k1
Hi Troy and I2C maintainer,
one thing I'd raise and seek I2C maintainer's suggestion, should this
driver introduce lock to protect multi context - non-atomic vs atomic vs
interrupt context, more than one i2c clients contend single controller?
On 14:07 Mon 29 Sep , Troy Mitchell wrote:
> This patch introduces I2C PIO functionality for the Spacemit K1 SoC,
> enabling the use of I2C in atomic context.
>
> Signed-off-by: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
> ---
> Changes in v3:
> - drop 1-5 patches (have been merged)
> - modify commit message
> - use readl_poll_timeout_atomic() in wait_pio_xfer()
> - use msecs_to_jiffies() when get PIO mode timeout value
> - factor out transfer state handling into spacemit_i2c_handle_state().
> - do not disable/enable the controller IRQ around PIO transfers.
> - consolidate spacemit_i2c_init() interrupt setup
> - rename is_pio -> use_pio
> - rename spacemit_i2c_xfer() -> spacemit_i2c_xfer_common()
> - rename spacemit_i2c_int_xfer() -> spacemit_i2c_xfer()
> - rename spacemit_i2c_pio_xfer() -> spacemit_i2c_pio_xfer_atomic()
> - call spacemit_i2c_err_check() in wait_pio_xfer() when write last byte
> - Link to v2: https://lore.kernel.org/r/20250925-k1-i2c-atomic-v2-0-46dc13311cda@linux.spacemit.com
>
> Changes in v2:
> - Patch 1/6:
> Patch 3/6:
> Patch 4/6:
> - nothing
> - Patch 2/6:
> - remove is_pio judgement in irq_handler()
> - Patch 5/6:
> - fix wrong comment
> - In spacemit_i2c_conditionally_reset_bus(), once the condition is met inside the loop, it should
> return directly instead of using break.
> - Patch 6/6:
> - add is_pio judgement in irq_handler()
> - use a fixed timeout value when PIO
> - use readl_poll_timeout() in spacemit_i2c_wait_bus_idle() when PIO
>
> - Link to v1: https://lore.kernel.org/r/20250827-k1-i2c-atomic-v1-0-e59bea02d680@linux.spacemit.com
> ---
> drivers/i2c/busses/i2c-k1.c | 206 ++++++++++++++++++++++++++++++++++----------
> 1 file changed, 161 insertions(+), 45 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-k1.c b/drivers/i2c/busses/i2c-k1.c
> index 6b918770e612e098b8ad17418f420d87c94df166..21c5dd56e71f5e59434767329fb84d50d5c04178 100644
> --- a/drivers/i2c/busses/i2c-k1.c
> +++ b/drivers/i2c/busses/i2c-k1.c
> @@ -97,6 +97,9 @@
>
> #define SPACEMIT_BUS_RESET_CLK_CNT_MAX 9
>
[snip]..
> +static void spacemit_i2c_handle_state(struct spacemit_i2c_dev *i2c);
> +static void spacemit_i2c_err_check(struct spacemit_i2c_dev *i2c);
please sort to avoid this kind declaration, if it's inevitable,
you can move to top, before the function, after macro
> +static int spacemit_i2c_wait_pio_xfer(struct spacemit_i2c_dev *i2c)
> +{
> + u32 msec = jiffies_to_msecs(i2c->adapt.timeout);
> + ktime_t timeout = ktime_add_ms(ktime_get(), msec);
> + int ret;
> +
> + while (i2c->unprocessed && ktime_compare(ktime_get(), timeout) < 0) {
> + udelay(10);
> + i2c->status = readl(i2c->base + SPACEMIT_ISR);
> +
> + spacemit_i2c_clear_int_status(i2c, i2c->status);
> +
> + if (!(i2c->status & SPACEMIT_SR_IRF) && !(i2c->status & SPACEMIT_SR_ITE))
this is hard to read
mask = SPACEMIT_SR_IRF | SPACEMIT_SR_ITE;
if ((i2c->status & mask) == 0)
..
> + continue;
> +
> + spacemit_i2c_handle_state(i2c);
> +
> + /*
> + * This is the last byte to write of the current message.
> + * If we do not wait here, control will proceed directly to start(),
> + * which would overwrite the current data.
> + */
> + if (!i2c->read && !i2c->unprocessed) {
> + ret = readl_poll_timeout_atomic(i2c->base + SPACEMIT_ISR,
> + i2c->status, i2c->status & SPACEMIT_SR_ITE,
> + 30, 1000);
> + if (ret)
> + return 0;
> + /*
> + * In read mode, err_check() in handle_state properly handles what happens
> + * after the MSD bit is set. For writes it is different: in interrupt mode,
> + * an ITE (write-empty) interrupt is triggered after the last byte, and the
> + * MSD-related handling takes place there. In PIO mode, however, we need to
> + * explicitly call err_check() to emulate this step, otherwise the next
> + * transfer will fail.
> + */
> + spacemit_i2c_err_check(i2c);
> + }
> + }
> +
> + if (i2c->unprocessed)
> + return 0;
> +
> + return 1;
> +}
> +
> static int spacemit_i2c_xfer_msg(struct spacemit_i2c_dev *i2c)
> {
> unsigned long time_left;
> @@ -310,10 +376,16 @@ static int spacemit_i2c_xfer_msg(struct spacemit_i2c_dev *i2c)
>
> reinit_completion(&i2c->complete);
>
> - spacemit_i2c_start(i2c);
..
> + if (i2c->use_pio) {
> + spacemit_i2c_start(i2c);
> +
> + time_left = spacemit_i2c_wait_pio_xfer(i2c);
> + } else {
> + spacemit_i2c_start(i2c);
> + time_left = wait_for_completion_timeout(&i2c->complete,
> + i2c->adapt.timeout);
> + }
suggest to distill a common function spacemit_i2c_wait_xfer_complete()
and converge above if/elselogic inside, which is more readable
>
> - time_left = wait_for_completion_timeout(&i2c->complete,
> - i2c->adapt.timeout);
> if (!time_left) {
> dev_err(i2c->dev, "msg completion timeout\n");
..
> spacemit_i2c_conditionally_reset_bus(i2c);
btw, not introduced in this patch, spacemit_i2c_reset() followed unconditionally after
spacemit_i2c_conditionally_reset_bus() which is very confusing
please double check the logic
> @@ -341,6 +413,9 @@ static bool spacemit_i2c_is_last_msg(struct spacemit_i2c_dev *i2c)
>
> static void spacemit_i2c_handle_write(struct spacemit_i2c_dev *i2c)
> {
> + if (!(i2c->status & SPACEMIT_SR_ITE))
> + return;
> +
> /* if transfer completes, SPACEMIT_ISR will handle it */
> if (i2c->status & SPACEMIT_SR_MSD)
> return;
[snip]..
>
> -static int spacemit_i2c_xfer(struct i2c_adapter *adapt, struct i2c_msg *msgs, int num)
> +static inline int
> +spacemit_i2c_xfer_common(struct i2c_adapter *adapt, struct i2c_msg *msgs, int num, bool use_pio)
> {
> struct spacemit_i2c_dev *i2c = i2c_get_adapdata(adapt);
> int ret;
>
> + i2c->use_pio = use_pio;
> +
> i2c->msgs = msgs;
> i2c->msg_num = num;
>
..
> - spacemit_i2c_calc_timeout(i2c);
> + if (!i2c->use_pio)
> + spacemit_i2c_calc_timeout(i2c);
> + else
> + i2c->adapt.timeout = msecs_to_jiffies(SPACEMIT_WAIT_TIMEOUT);
suggest merge "if else" into spacemit_i2c_calc_timeout(), same as previous suggestion
>
> spacemit_i2c_init(i2c);
>
> spacemit_i2c_enable(i2c);
>
> + /* To avoid being affected by the state of the previous transfer */
> + spacemit_i2c_clear_int_status(i2c, SPACEMIT_I2C_INT_STATUS_MASK);
> +
I've not see my previous comment has been addressed!
> ret = spacemit_i2c_wait_bus_idle(i2c);
> if (!ret) {
> ret = spacemit_i2c_xfer_msg(i2c);
> @@ -506,11 +611,21 @@ static int spacemit_i2c_xfer(struct i2c_adapter *adapt, struct i2c_msg *msgs, in
>
> if (ret == -ETIMEDOUT || ret == -EAGAIN)
> dev_err(i2c->dev, "i2c transfer failed, ret %d err 0x%lx\n",
> - ret, i2c->status & SPACEMIT_SR_ERR);
> + ret, i2c->status & SPACEMIT_SR_ERR);
>
have to say, I personally don't like those unrelated changes, which
makes people review the patch even difficult
> return ret < 0 ? ret : num;
> }
>
> +static int spacemit_i2c_xfer(struct i2c_adapter *adapt, struct i2c_msg *msgs, int num)
> +{
> + return spacemit_i2c_xfer_common(adapt, msgs, num, false);
> +}
> +
> +static int spacemit_i2c_pio_xfer_atomic(struct i2c_adapter *adapt, struct i2c_msg *msgs, int num)
> +{
> + return spacemit_i2c_xfer_common(adapt, msgs, num, true);
> +}
> +
atomic API should not call sleepable function, please check this
spacemit_i2c_pio_xfer_atomic() ->
spacemit_i2c_xfer_common() ->
spacemit_i2c_xfer_msg() ->
spacemit_i2c_conditionally_reset_bus() ->
usleep_range()
spacemit_i2c_check_bus_release() ->
usleep_range()
they are in err handle path, but still need to take care with caution
--
Yixun Lan (dlan)
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