From: Thierry Reding treding@nvidia.com
The SOR resets are exclusively shared with the SOR power domain. This means that exclusive access can only be granted temporarily and in order for that to work, a rigorous sequence must be observed. To ensure that a single consumer gets exclusive access to a reset, each consumer must implement a rigorous protocol using the reset_control_acquire() and reset_control_release() functions.
However, these functions alone don't provide any guarantees at the system level. Drivers need to ensure that the only a single consumer has access to the reset at the same time. In order for the SOR to be able to exclusively access its reset, it must therefore ensure that the SOR power domain is not powered off by holding on to a runtime PM reference to that power domain across the reset assert/deassert operation.
This used to work fine by accident, but was revealed when recently more devices started to rely on the SOR power domain.
Fixes: 11c632e1cfd3 ("drm/tegra: sor: Implement acquire/release for reset") Reported-by: Jonathan Hunter jonathanh@nvidia.com Signed-off-by: Thierry Reding treding@nvidia.com --- drivers/gpu/drm/tegra/sor.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/gpu/drm/tegra/sor.c b/drivers/gpu/drm/tegra/sor.c index f02a035dda45..7b88261f57bb 100644 --- a/drivers/gpu/drm/tegra/sor.c +++ b/drivers/gpu/drm/tegra/sor.c @@ -3115,6 +3115,12 @@ static int tegra_sor_init(struct host1x_client *client) * kernel is possible. */ if (sor->rst) { + err = pm_runtime_resume_and_get(sor->dev); + if (err < 0) { + dev_err(sor->dev, "failed to get runtime PM: %d\n", err); + return err; + } + err = reset_control_acquire(sor->rst); if (err < 0) { dev_err(sor->dev, "failed to acquire SOR reset: %d\n", @@ -3148,6 +3154,7 @@ static int tegra_sor_init(struct host1x_client *client) }
reset_control_release(sor->rst); + pm_runtime_put(sor->dev); }
err = clk_prepare_enable(sor->clk_safe);