On Mon, Apr 11, 2022 at 03:21:07PM +0200, AngeloGioacchino Del Regno wrote: > 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> Applied to for-next, thanks!
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