[PATCH] drm/bridge: analogix dp: Fix runtime PM state in get_modes() callback

[Archit Taneja]

On 11/21/2017 01:19 PM, Marek Szyprowski wrote:
> get_modes() callback might be called asynchronously from the DRM core and
> it is not synchronized with bridge_enable(), which sets proper runtime PM
> state of the main DP device. Fix this by calling pm_runtime_get_sync()
> before calling drm_get_edid(), which in turn calls drm_dp_i2c_xfer() and
> analogix_dp_transfer() to ensure that main DP device is runtime active
> when doing any access to its registers.

Looks good to me. Would be nice to get an ack from rockchip too. Will queue it
to drm-misc-fixes (so that it's merged for 4.15-rc2) if no one has any
objections.

Thanks,
Archit

> 
> This fixes the following kernel issue on Samsung Exynos5250 Snow board:
> Unhandled fault: imprecise external abort (0x406) at 0x00000000
> pgd = c0004000
> [00000000] *pgd=00000000
> Internal error: : 406 [#1] PREEMPT SMP ARM
> Modules linked in:
> CPU: 0 PID: 62 Comm: kworker/0:2 Not tainted 4.13.0-rc2-00364-g4a97a3da420b #3357
> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> Workqueue: events output_poll_execute
> task: edc14800 task.stack: edcb2000
> PC is at analogix_dp_transfer+0x15c/0x2fc
> LR is at analogix_dp_transfer+0x134/0x2fc
> pc : [<c0468538>]    lr : [<c0468510>]    psr: 60000013
> sp : edcb3be8  ip : 0000002a  fp : 00000001
> r10: 00000000  r9 : edcb3cd8  r8 : edcb3c40
> r7 : 00000000  r6 : edd3b380  r5 : edd3b010  r4 : 00000064
> r3 : 00000000  r2 : f0ad3000  r1 : edcb3c40  r0 : edd3b010
> Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
> Control: 10c5387d  Table: 4000406a  DAC: 00000051
> Process kworker/0:2 (pid: 62, stack limit = 0xedcb2210)
> Stack: (0xedcb3be8 to 0xedcb4000)
> [<c0468538>] (analogix_dp_transfer) from [<c0424ba4>] (drm_dp_i2c_do_msg+0x8c/0x2b4)
> [<c0424ba4>] (drm_dp_i2c_do_msg) from [<c0424e64>] (drm_dp_i2c_xfer+0x98/0x214)
> [<c0424e64>] (drm_dp_i2c_xfer) from [<c057b2d8>] (__i2c_transfer+0x140/0x29c)
> [<c057b2d8>] (__i2c_transfer) from [<c057b4a4>] (i2c_transfer+0x70/0xe4)
> [<c057b4a4>] (i2c_transfer) from [<c0441de4>] (drm_do_probe_ddc_edid+0xb4/0x114)
> [<c0441de4>] (drm_do_probe_ddc_edid) from [<c0441e5c>] (drm_probe_ddc+0x18/0x28)
> [<c0441e5c>] (drm_probe_ddc) from [<c0445728>] (drm_get_edid+0x124/0x2d4)
> [<c0445728>] (drm_get_edid) from [<c0465ea0>] (analogix_dp_get_modes+0x90/0x114)
> [<c0465ea0>] (analogix_dp_get_modes) from [<c0425e8c>] (drm_helper_probe_single_connector_modes+0x198/0x68c)
> [<c0425e8c>] (drm_helper_probe_single_connector_modes) from [<c04325d4>] (drm_setup_crtcs+0x1b4/0xd18)
> [<c04325d4>] (drm_setup_crtcs) from [<c04344a8>] (drm_fb_helper_hotplug_event+0x94/0xd0)
> [<c04344a8>] (drm_fb_helper_hotplug_event) from [<c0425a50>] (drm_kms_helper_hotplug_event+0x24/0x28)
> [<c0425a50>] (drm_kms_helper_hotplug_event) from [<c04263ec>] (output_poll_execute+0x6c/0x174)
> [<c04263ec>] (output_poll_execute) from [<c0136f18>] (process_one_work+0x188/0x3fc)
> [<c0136f18>] (process_one_work) from [<c01371f4>] (worker_thread+0x30/0x4b8)
> [<c01371f4>] (worker_thread) from [<c013daf8>] (kthread+0x128/0x164)
> [<c013daf8>] (kthread) from [<c0108510>] (ret_from_fork+0x14/0x24)
> Code: 0a000002 ea000009 e2544001 0a00004a (e59537c8)
> ---[ end trace cddc7919c79f7878 ]---
> 
> Reported-by: Misha Komarovskiy <zombah at gmail.com>
> CC: stable at vger.kernel.org # v4.10+
> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> ---
> This issue was there from the beginning, but recent changes to DRM
> core revealed it. It makes sense to backport it to patch f0a8b49c03d2
> ("drm/bridge: analogix dp: Fix runtime PM state on driver bind"),
> which fixed similar issue on driver bind, thus I've marked it for
> stable v4.10+.
> 
> Best regards
> Marek Szyprowski
> Samsung R&D Institute Poland
> ---
>   drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> index 5dd3f1cd074a..a8905049b9da 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> @@ -946,7 +946,9 @@ static int analogix_dp_get_modes(struct drm_connector *connector)
>   			return 0;
>   		}
>   
> +		pm_runtime_get_sync(dp->dev);
>   		edid = drm_get_edid(connector, &dp->aux.ddc);
> +		pm_runtime_put(dp->dev);
>   		if (edid) {
>   			drm_mode_connector_update_edid_property(&dp->connector,
>   								edid);
> 

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