Re: [PATCH] memory: samsung: exynos5422-dmc: propagate error from exynos5_counters_get()

From: Lukasz Luba
Date: Tue Aug 04 2020 - 05:11:12 EST

Hi Marek,

On 8/4/20 7:12 AM, Marek Szyprowski wrote:
exynos5_counters_get() might fail with -EPROBE_DEFER if the driver for
devfreq event counter is not yet probed. Propagate that error value to
the caller to ensure that the exynos5422-dmc driver will be probed again
when devfreq event contuner is available.

This fixes boot hang if both exynos5422-dmc and exynos-ppmu drivers are
compiled as modules.

Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
drivers/memory/samsung/exynos5422-dmc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/memory/samsung/exynos5422-dmc.c b/drivers/memory/samsung/exynos5422-dmc.c
index b9c7956e5031..639811a3eecb 100644
--- a/drivers/memory/samsung/exynos5422-dmc.c
+++ b/drivers/memory/samsung/exynos5422-dmc.c
@@ -914,7 +914,7 @@ static int exynos5_dmc_get_status(struct device *dev,
} else {
ret = exynos5_counters_get(dmc, &load, &total);
if (ret < 0)
- return -EINVAL;
+ return ret;
/* To protect from overflow, divide by 1024 */
stat->busy_time = load >> 10;

Thank you for the patch, LGTM.
Some questions are still there, though. The function
exynos5_performance_counters_init() should capture that the counters
couldn't be enabled or set. So the functions:
exynos5_counters_enable_edev() and exynos5_counters_set_event()
must pass gently because devfreq device is registered.
Then devfreq checks device status, and reaches the state when
counters 'get' function returns that they are not ready...

If that is a kind of 2-stage initialization, maybe we should add
another 'check' in the exynos5_performance_counters_init() and call
the devfreq_event_get_event() to make sure that we are ready to go,
otherwise return ret from that function (which is probably EPROBE_DEFER)
and not register the devfreq device.

Marek do want to submit such patch or I should bake it and submit on top
of this patch?

Could you tell me how I can reproduce this? Do you simply load one
module after another (exynos-ppmu than exynos5422-dmc) or in parallel?