[PATCH] ASoC: qcom: Actually clear DMA interrupt register for HDMI

[PATCH] ASoC: qcom: Actually clear DMA interrupt register for HDMI

[Stephen Boyd]

In commit da0363f7bfd3 ("ASoC: qcom: Fix for DMA interrupt clear reg
overwriting") we changed regmap_write() to regmap_update_bits() so that
we can avoid overwriting bits that we didn't intend to modify.
Unfortunately this change breaks the case where a register is writable
but not readable, which is exactly how the HDMI irq clear register is
designed (grep around LPASS_HDMITX_APP_IRQCLEAR_REG to see how it's
write only). That's because regmap_update_bits() tries to read the
register from the hardware and if it isn't readable it looks in the
regmap cache to see what was written there last time to compare against
what we want to write there. Eventually, we're unable to modify this
register at all because the bits that we're trying to set are already
set in the cache.

This is doubly bad for the irq clear register because you have to write
the bit to clear an interrupt. Given the irq is level triggered, we see
an interrupt storm upon plugging in an HDMI cable and starting audio
playback. The irq storm is so great that performance degrades
significantly, leading to CPU soft lockups.

Fix it by using regmap_write_bits() so that we really do write the bits
in the clear register that we want to. This brings the number of irqs
handled by lpass_dma_interrupt_handler() down from ~150k/sec to ~10/sec.

Fixes: da0363f7bfd3 ("ASoC: qcom: Fix for DMA interrupt clear reg overwriting")
Cc: Srinivasa Rao Mandadapu <srivasam@codeaurora.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
 sound/soc/qcom/lpass-platform.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/sound/soc/qcom/lpass-platform.c b/sound/soc/qcom/lpass-platform.c
index a59e9d20cb46..4b1773c1fb95 100644
--- a/sound/soc/qcom/lpass-platform.c
+++ b/sound/soc/qcom/lpass-platform.c
@@ -524,7 +524,7 @@ static int lpass_platform_pcmops_trigger(struct snd_soc_component *component,
 			return -EINVAL;
 		}
 
-		ret = regmap_update_bits(map, reg_irqclr, val_irqclr, val_irqclr);
+		ret = regmap_write_bits(map, reg_irqclr, val_irqclr, val_irqclr);
 		if (ret) {
 			dev_err(soc_runtime->dev, "error writing to irqclear reg: %d\n", ret);
 			return ret;
@@ -665,7 +665,7 @@ static irqreturn_t lpass_dma_interrupt_handler(
 	return -EINVAL;
 	}
 	if (interrupts & LPAIF_IRQ_PER(chan)) {
-		rv = regmap_update_bits(map, reg, mask, (LPAIF_IRQ_PER(chan) | val));
+		rv = regmap_write_bits(map, reg, mask, (LPAIF_IRQ_PER(chan) | val));
 		if (rv) {
 			dev_err(soc_runtime->dev,
 				"error writing to irqclear reg: %d\n", rv);
@@ -676,7 +676,7 @@ static irqreturn_t lpass_dma_interrupt_handler(
 	}
 
 	if (interrupts & LPAIF_IRQ_XRUN(chan)) {
-		rv = regmap_update_bits(map, reg, mask, (LPAIF_IRQ_XRUN(chan) | val));
+		rv = regmap_write_bits(map, reg, mask, (LPAIF_IRQ_XRUN(chan) | val));
 		if (rv) {
 			dev_err(soc_runtime->dev,
 				"error writing to irqclear reg: %d\n", rv);
@@ -688,7 +688,7 @@ static irqreturn_t lpass_dma_interrupt_handler(
 	}
 
 	if (interrupts & LPAIF_IRQ_ERR(chan)) {
-		rv = regmap_update_bits(map, reg, mask, (LPAIF_IRQ_ERR(chan) | val));
+		rv = regmap_write_bits(map, reg, mask, (LPAIF_IRQ_ERR(chan) | val));
 		if (rv) {
 			dev_err(soc_runtime->dev,
 				"error writing to irqclear reg: %d\n", rv);

base-commit: dfd42facf1e4ada021b939b4e19c935dcdd55566
-- 
https://chromeos.dev

Re: [PATCH] ASoC: qcom: Actually clear DMA interrupt register for HDMI

[Mark Brown]

On Wed, 9 Feb 2022 15:25:20 -0800, Stephen Boyd wrote:
> In commit da0363f7bfd3 ("ASoC: qcom: Fix for DMA interrupt clear reg
> overwriting") we changed regmap_write() to regmap_update_bits() so that
> we can avoid overwriting bits that we didn't intend to modify.
> Unfortunately this change breaks the case where a register is writable
> but not readable, which is exactly how the HDMI irq clear register is
> designed (grep around LPASS_HDMITX_APP_IRQCLEAR_REG to see how it's
> write only). That's because regmap_update_bits() tries to read the
> register from the hardware and if it isn't readable it looks in the
> regmap cache to see what was written there last time to compare against
> what we want to write there. Eventually, we're unable to modify this
> register at all because the bits that we're trying to set are already
> set in the cache.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-linus

Thanks!

[1/1] ASoC: qcom: Actually clear DMA interrupt register for HDMI
      commit: c8d251f51ee61df06ee0e419348d8c9160bbfb86

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark