Re: [PATCH 2/2] drm/msm/dpu: Remove dynamic allocation from atomic context

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On 10/22/2021 10:20 AM, Rob Clark wrote:
From: Rob Clark <robdclark@xxxxxxxxxxxx>

We know the upper bound on # of mixers (ie. two), so lets just allocate
this on the stack.

Fixes:

    BUG: sleeping function called from invalid context at include/linux/sched/mm.h:201
    in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/0
    INFO: lockdep is turned off.
    irq event stamp: 43642
    hardirqs last  enabled at (43641): [<ffffffe24dd276bc>] cpuidle_enter_state+0x158/0x25c
    hardirqs last disabled at (43642): [<ffffffe24dfff450>] enter_el1_irq_or_nmi+0x10/0x1c
    softirqs last  enabled at (43620): [<ffffffe24d4103fc>] __do_softirq+0x1e4/0x464
    softirqs last disabled at (43615): [<ffffffe24d48bd90>] __irq_exit_rcu+0x104/0x150
    CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W         5.15.0-rc3-debug+ #105
    Hardware name: Google Lazor (rev1 - 2) with LTE (DT)
    Call trace:
     dump_backtrace+0x0/0x18c
     show_stack+0x24/0x30
     dump_stack_lvl+0xa0/0xd4
     dump_stack+0x18/0x34
     ___might_sleep+0x1e0/0x1f0
     __might_sleep+0x78/0x8c
     slab_pre_alloc_hook.constprop.0+0x48/0x6c
     __kmalloc+0xc8/0x21c
     dpu_crtc_vblank_callback+0x158/0x1f8
     dpu_encoder_vblank_callback+0x70/0xc4
     dpu_encoder_phys_vid_vblank_irq+0x50/0x12c
     dpu_core_irq+0x1bc/0x1d0
     dpu_irq+0x1c/0x28
     msm_irq+0x34/0x40
     __handle_irq_event_percpu+0x15c/0x308
     handle_irq_event_percpu+0x3c/0x90
     handle_irq_event+0x54/0x98
     handle_level_irq+0xa0/0xd0
     handle_irq_desc+0x2c/0x44
     generic_handle_domain_irq+0x28/0x34
     dpu_mdss_irq+0x90/0xe8
     handle_irq_desc+0x2c/0x44
     handle_domain_irq+0x54/0x80
     gic_handle_irq+0xd4/0x148
     call_on_irq_stack+0x2c/0x54
     do_interrupt_handler+0x4c/0x64
     el1_interrupt+0x30/0xd0
     el1h_64_irq_handler+0x18/0x24
     el1h_64_irq+0x78/0x7c
     arch_local_irq_enable+0xc/0x14
     cpuidle_enter+0x44/0x5c
     do_idle+0x248/0x268
     cpu_startup_entry+0x30/0x48
     rest_init+0x188/0x19c
     arch_call_rest_init+0x1c/0x28
     start_kernel+0x704/0x744
     __primary_switched+0xc0/0xc8

Fixes: 78d9b458cc21 ("drm/msm/dpu: Add CRC support for DPU")
Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
---
  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 16 +++++-----------
  1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
index 0ae397044310..80c0ae688734 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
@@ -182,21 +182,19 @@ static int dpu_crtc_get_crc(struct drm_crtc *crtc)
  {
  	struct dpu_crtc_state *crtc_state;
  	struct dpu_crtc_mixer *m;
-	u32 *crcs;
+	u32 crcs[CRTC_DUAL_MIXERS];
int i = 0;
  	int rc = 0;
crtc_state = to_dpu_crtc_state(crtc->state);
-	crcs = kcalloc(crtc_state->num_mixers, sizeof(*crcs), GFP_KERNEL);
- if (!crcs)
-		return -ENOMEM;
+	static_assert(ARRAY_SIZE(crcs) == ARRAY_SIZE(crtc_state->mixers));

Getting a C90 compiler warning for static_assert():

    In file included from ./include/linux/bits.h:22,
                    from ./include/linux/bitops.h:6,
                    from ./include/linux/kernel.h:12,
                    from ./include/linux/list.h:9,
                    from ./include/linux/wait.h:7,
                    from ./include/linux/wait_bit.h:8,
                    from ./include/linux/fs.h:6,
                    from ./include/linux/debugfs.h:15,
                    from drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c:10:
    drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c: In function ‘dpu_crtc_get_crc’:     ./include/linux/build_bug.h:78:41: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]         78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
        |                                         ^~~~~~~~~~~~~~
    ./include/linux/build_bug.h:77:34: note: in expansion of macro ‘__static_assert’         77 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr)
        |                                  ^~~~~~~~~~~~~~~
    drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c:192:2: note: in expansion of macro ‘static_assert’     192 |  static_assert(ARRAY_SIZE(crcs) == ARRAY_SIZE(crtc_state->mixers));
        |  ^~~~~~~~~~~~~

Can be fixed by moving the static_assert() before `crtc_state = ...`

Thanks,

Jessica Zhang

  	/* Skip first 2 frames in case of "uncooked" CRCs */
  	if (crtc_state->crc_frame_skip_count < 2) {
  		crtc_state->crc_frame_skip_count++;
-		goto cleanup;
+		return 0;
  	}
for (i = 0; i < crtc_state->num_mixers; ++i) {
@@ -210,16 +208,12 @@ static int dpu_crtc_get_crc(struct drm_crtc *crtc)
if (rc) {
  			DRM_DEBUG_DRIVER("MISR read failed\n");
-			goto cleanup;
+			return rc;
  		}
  	}
- rc = drm_crtc_add_crc_entry(crtc, true,
+	return drm_crtc_add_crc_entry(crtc, true,
  			drm_crtc_accurate_vblank_count(crtc), crcs);
-
-cleanup:
-	kfree(crcs);
-	return rc;
  }
static bool dpu_crtc_get_scanout_position(struct drm_crtc *crtc,



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