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070e64dc1b
Devices that make up DPU, i.e. graphics card, request their interrupts from this "virtual" interrupt chip. The interrupt chip builds upon a GIC SPI interrupt that raises high when any of the interrupts in the DPU's irq status register are triggered. From the kernel's perspective this is a chained irq chip, so requesting a flow handler for the GIC SPI and then calling generic IRQ handling code from that irq handler is not completely proper. It's better to convert this to a chained irq so that the GIC SPI irq doesn't appear in /proc/interrupts, can't have CPU affinity changed, and won't be accounted for with irq stats. Doing this also silences a recursive lockdep warning because we can specify a different lock class for the chained interrupts, silencing a warning that is easy to see with 'threadirqs' on the kernel commandline. WARNING: inconsistent lock state 4.19.10 #76 Tainted: G W -------------------------------- inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. irq/40-dpu_mdss/203 [HC0[0]:SC0[2]:HE1:SE0] takes: 0000000053ea9021 (&irq_desc_lock_class){?.-.}, at: handle_level_irq+0x34/0x26c {IN-HARDIRQ-W} state was registered at: lock_acquire+0x244/0x360 _raw_spin_lock+0x64/0xa0 handle_fasteoi_irq+0x54/0x2ec generic_handle_irq+0x44/0x5c __handle_domain_irq+0x9c/0x11c gic_handle_irq+0x208/0x260 el1_irq+0xb4/0x130 arch_cpu_idle+0x178/0x3cc default_idle_call+0x3c/0x54 do_idle+0x1a8/0x3dc cpu_startup_entry+0x24/0x28 rest_init+0x240/0x270 start_kernel+0x5a8/0x6bc irq event stamp: 18 hardirqs last enabled at (17): [<ffffff9042385e80>] _raw_spin_unlock_irq+0x40/0xc0 hardirqs last disabled at (16): [<ffffff904237a1f4>] __schedule+0x20c/0x1bbc softirqs last enabled at (0): [<ffffff9040f318d0>] copy_process+0xb50/0x3964 softirqs last disabled at (18): [<ffffff9041036364>] local_bh_disable+0x8/0x20 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&irq_desc_lock_class); <Interrupt> lock(&irq_desc_lock_class); *** DEADLOCK *** no locks held by irq/40-dpu_mdss/203. stack backtrace: CPU: 0 PID: 203 Comm: irq/40-dpu_mdss Tainted: G W 4.19.10 #76 Call trace: dump_backtrace+0x0/0x2f8 show_stack+0x20/0x2c __dump_stack+0x20/0x28 dump_stack+0xcc/0x10c mark_lock+0xbe0/0xe24 __lock_acquire+0x4cc/0x2708 lock_acquire+0x244/0x360 _raw_spin_lock+0x64/0xa0 handle_level_irq+0x34/0x26c generic_handle_irq+0x44/0x5c dpu_mdss_irq+0x64/0xec irq_forced_thread_fn+0x58/0x9c irq_thread+0x120/0x1dc kthread+0x248/0x260 ret_from_fork+0x10/0x18 ------------[ cut here ]------------ irq 169 handler irq_default_primary_handler+0x0/0x18 enabled interrupts Cc: Sean Paul <seanpaul@chromium.org> Cc: Jordan Crouse <jcrouse@codeaurora.org> Cc: Jayant Shekhar <jshekhar@codeaurora.org> Cc: Rajesh Yadav <ryadav@codeaurora.org> Cc: Jeykumar Sankaran <jsanka@codeaurora.org> Signed-off-by: Stephen Boyd <swboyd@chromium.org> Signed-off-by: Sean Paul <seanpaul@chromium.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.