On 09/21/2016 06:28 PM, Maciej S. Szmigiero wrote: > Hi Marek, Hi! > On 19.09.2016 21:30, Marek Vasut wrote: >> Same as commit ce492b3b8f99cf9d2f807ec22d8805c996a09503 >> Subject: drm/fsl-dcu: use flat regmap cache >> >> Using flat regmap cache instead of RB-tree to avoid the following >> lockdep warning on driver load: >> WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2871 lockdep_trace_alloc+0x104/0x128 >> DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)) >> >> The RB-tree regmap cache needs to allocate new space on first >> writes. > > That's why SSI driver had .num_reg_defaults_raw set in regmap config. > With this set and .reg_defaults_raw unset regcache_hw_init() will read > existing register content which then will be used to populate cache > (and so allocate RB tree nodes) at regcache initialization time. OK > This means that allocation of new cache RB tree nodes should never happen > during actual write. > If you get a warning that it happened then maybe there is a write to > some register not covered by .num_reg_defaults_raw - this should be > fixed. I might be blind, but I really don't see that. I just discussed it with Mark and he thinks the same. I will revisit this one more time. > The problem with flat cache is that it is zero-initialized, that is, > all registers are assumed to contain zeros by default. > This is generally not true in case of SSI so reads from and bit updates > in non-volatile registers will corrupt their value. This will let the driver init the hardware into a well-defined state. Are there any bits in the SSI config registers which we must preserve? > You can also refer to discussion when .num_reg_defaults_raw was first > added here: > http://www.gossamer-threads.com/lists/linux/kernel/2330573 Thanks! > Maciej > -- Best regards, Marek Vasut _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
