Il 11/04/22 15:21, AngeloGioacchino Del Regno ha scritto:
Especially (but not only) during probe, it may happen that multiple devices are communicating via i2c (or multiple i2c busses) and sometimes while others are probing asynchronously. For example, a Cr50 TPM may be filling entropy (or userspace may be reading random data) while the rt5682 (i2c) codec driver reads/sets some registers, like while getting/setting a clock's rate, which happens both during probe and during system operation. In this driver, the mtk_i2c_transfer() function (which is the i2c .master_xfer() callback) was granularly managing the clocks by performing a clk_bulk_prepare_enable() to start them and its inverse. This is not only creating possible circular locking dependencies in the some cases (like former explanation), but it's also suboptimal, as clk_core prepare/unprepare operations are using mutex locking, which creates a bit of unwanted overhead (for example, i2c trackpads will call master_xfer() every few milliseconds!). With this commit, we avoid both the circular locking and additional overhead by changing how we handle the clocks in this driver: - Prepare the clocks during probe (and PM resume) - Enable/disable clocks in mtk_i2c_transfer() - Unprepare the clocks only for driver removal (and PM suspend) For the sake of providing a full explanation: during probe, the clocks are not only prepared but also enabled, as this is needed for some hardware initialization but, after that, we are disabling but not unpreparing them, leaving an expected state for the aforementioned clock handling strategy. Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx> Tested-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>
Hello, this is a friendly ping to not let this be forgotten. Cheers, Angelo
--- v2: Fixed typos in commit description drivers/i2c/busses/i2c-mt65xx.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
