diff mbox series

[v3,1/1] i2c: lpi2c: Avoid calling clk_get_rate during transfer

Message ID 20240422113629.1629891-1-alexander.stein@ew.tq-group.com (mailing list archive)
State New, archived
Headers show
Series [v3,1/1] i2c: lpi2c: Avoid calling clk_get_rate during transfer | expand

Commit Message

Alexander Stein April 22, 2024, 11:36 a.m. UTC 
Instead of repeatedly calling clk_get_rate for each transfer, lock
the clock rate and cache the value.
A deadlock has been observed while adding tlv320aic32x4 audio codec to
the system. When this clock provider adds its clock, the clk mutex is
locked already, it needs to access i2c, which in return needs the mutex
for clk_get_rate as well.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
---
This is an alternative, lightweight approach replacing the patch [1].
The issue to address is still removing the call to clk_get_rate() during each
transfer, which might reuslt in a deadlock. lockdep also complains about this
call chain.
The dependency from v2 has already been merged in commit b0cde62e4c548
("clk: Add a devm variant of clk_rate_exclusive_get()").

Instead of adding a clock notifier, lock the peripheral clock rate and cache
the peripheral clock rate.
Currently LPI2C is available in the following SoC:
* i.MX7ULP
* i.MX8ULP
* i.MX8DXL
* i.MX8X
* i.MX8
* i.MX93

Additionally I expect both i.MX91 and i.MX95 to also use this driver.

This patch assumes the parent clock rate never changes. This is apparently true
for i.MX93 as each I2C has it's own lpi2c*_root clock. On i.MX8 and i.MX8X
clocks are managed by SCU with it's own dedicated firmware. I can't say if the
clock never changes though. I have no idea about the other SoC.

Changes in v3:
* Rebased to next-20240422

Changes in v2:
* Removed redundent clk_rate check in lpi2c_imx_config (I opted to keep
  the local variable to not extent the calculation code lines)
* Collected R-b

Best regards,
Alexander

[1] https://lore.kernel.org/all/20240110120556.519800-1-alexander.stein@ew.tq-group.com/

 drivers/i2c/busses/i2c-imx-lpi2c.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

Comments

Uwe Kleine-König April 22, 2024, 3:42 p.m. UTC | #1 
Hello Alexander,

On Mon, Apr 22, 2024 at 01:36:29PM +0200, Alexander Stein wrote:
> The dependency from v2 has already been merged in commit b0cde62e4c548
> ("clk: Add a devm variant of clk_rate_exclusive_get()").

Note that you might also need 7f1dd39aedfccf60772328c5b88d56dbd39954c3
which is part of v6.9-rc5.

Best regards
Uwe
Andi Shyti April 22, 2024, 10:25 p.m. UTC | #2 
Hi Uwe,

On Mon, Apr 22, 2024 at 05:42:20PM +0200, Uwe Kleine-König wrote:
> On Mon, Apr 22, 2024 at 01:36:29PM +0200, Alexander Stein wrote:
> > The dependency from v2 has already been merged in commit b0cde62e4c548
> > ("clk: Add a devm variant of clk_rate_exclusive_get()").
> 
> Note that you might also need 7f1dd39aedfccf60772328c5b88d56dbd39954c3
> which is part of v6.9-rc5.

it's fine... I have rebased all my branches on top of v6.9-rc5.

Thanks!

Andi
Andi Shyti April 22, 2024, 10:51 p.m. UTC | #3 
Hi

On Mon, 22 Apr 2024 13:36:29 +0200, Alexander Stein wrote:
> Instead of repeatedly calling clk_get_rate for each transfer, lock
> the clock rate and cache the value.
> A deadlock has been observed while adding tlv320aic32x4 audio codec to
> the system. When this clock provider adds its clock, the clk mutex is
> locked already, it needs to access i2c, which in return needs the mutex
> for clk_get_rate as well.
> 
> [...]

Applied to i2c/i2c-host on

git://git.kernel.org/pub/scm/linux/kernel/git/andi.shyti/linux.git

Thank you,
Andi

Patches applied
===============
[1/1] i2c: lpi2c: Avoid calling clk_get_rate during transfer
      commit: 7ec84d4d55504710a828047d079cb22f12d4133f
diff mbox series

Patch

diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
index 6d72e4e126dde..36e8f6196a87b 100644
--- a/drivers/i2c/busses/i2c-imx-lpi2c.c
+++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
@@ -99,6 +99,7 @@  struct lpi2c_imx_struct {
 	__u8			*rx_buf;
 	__u8			*tx_buf;
 	struct completion	complete;
+	unsigned long		rate_per;
 	unsigned int		msglen;
 	unsigned int		delivered;
 	unsigned int		block_data;
@@ -212,9 +213,7 @@  static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
 
 	lpi2c_imx_set_mode(lpi2c_imx);
 
-	clk_rate = clk_get_rate(lpi2c_imx->clks[0].clk);
-	if (!clk_rate)
-		return -EINVAL;
+	clk_rate = lpi2c_imx->rate_per;
 
 	if (lpi2c_imx->mode == HS || lpi2c_imx->mode == ULTRA_FAST)
 		filt = 0;
@@ -611,6 +610,20 @@  static int lpi2c_imx_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	/*
+	 * Lock the parent clock rate to avoid getting parent clock upon
+	 * each transfer
+	 */
+	ret = devm_clk_rate_exclusive_get(&pdev->dev, lpi2c_imx->clks[0].clk);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret,
+				     "can't lock I2C peripheral clock rate\n");
+
+	lpi2c_imx->rate_per = clk_get_rate(lpi2c_imx->clks[0].clk);
+	if (!lpi2c_imx->rate_per)
+		return dev_err_probe(&pdev->dev, -EINVAL,
+				     "can't get I2C peripheral clock rate\n");
+
 	pm_runtime_set_autosuspend_delay(&pdev->dev, I2C_PM_TIMEOUT);
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_get_noresume(&pdev->dev);