Am 31.12.18 um 18:50 schrieb Mark Brown: > On Sun, Dec 30, 2018 at 11:55:46AM +0100, Andreas Färber wrote: >> Given that observed symptoms were CPU stalls, workqueue hangs and RCU >> problems, requiring a power-cycle to recover, I wonder whether we are >> running into some atomic/locking issue with clk_enable()? Is it valid at >> all to use SPI/regmap for clk_enable()? If it is, is there a known issue >> specific to spi-sun6i (A64) in 4.20.0? >> I already tried setting .disable_locking = true in both regmap_configs. >> Any suggestions how to further debug? > > You can't use SPI for clk_enable(), clk_enable() needs to be doable in > atomic context since we need to wait for the bus operations to complete > (you can start SPI transfers in atomic context but you still need to > wait for them to complete). Any clocks that are only accessible via a > slow bus like I2C or SPI need to do the enable/disable in the > prepare/unprepare operations which aren't done in atomic context. > > regmap can be used in atomic contexts, though you need to configure it > to use spinlocks instead of mutexes and ensure that no register cache > allocations happen during I/O (eg, by providing defaults for all > registers or by not using a cache). We have .cache_type = REGCACHE_NONE on both bus and spi regmap_configs. I moved the regmap_field_write() from .enable to .prepare and set .fast_io = true on both regmap_configs to force using spinlocks, but same hang as in .enable before... And same if I set .disable_locking = true on both. Given that it works with one SPI driver and not with the other, independent of the locking options applied, I assume my symptoms are not a regmap-layer issue. Is it allowed during a .prepare operation to call the mentioned clk_get_rate(), which ends up calling clk_prepare_lock()? According to my debug output in spi-sun6i.c our hanging regmap_field_write() ends up calling sun6i_transfer_one() three times, the first two look okay, but the third one doesn't make it past the clk_get_rate() or following if block. [But for now some fireworks...] Regards, Andreas -- SUSE Linux GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg)
