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    SubjectRe: parallel panel display stopped working
    On Fri, Jul 9, 2021 at 5:40 PM Andy Shevchenko
    <andy.shevchenko@gmail.com> wrote:
    >
    > Parallel (4 bits) panel display stopped working.
    > I have no time right now to bisect but I have noticed there was quite
    > a pile of patches from Lars to the driver recently (yeah, it seems for
    > a few months I haven't run my tests against the AUX display driver).
    >
    > I believe the issue is there somewhere.
    >
    > Moreover on the removal I have got an oops
    >
    > [ 218.825445] kernel tried to execute NX-protected page - exploit
    > attempt? (uid: 0)
    > [ 218.832965] BUG: unable to handle page fault for address: ffff8f8f06559dc0
    > [ 218.839863] #PF: supervisor instruction fetch in kernel mode
    > [ 218.845540] #PF: error_code(0x0011) - permissions violation
    > [ 218.851132] PGD e601067 P4D e601067 PUD e602067 PMD 645a063 PTE
    > 8000000006559063
    > [ 218.858587] Oops: 0011 [#1] SMP PTI
    > [ 218.862099] CPU: 0 PID: 7 Comm: kworker/u4:0 Tainted: G C
    > 5.13.0+ #23
    > [ 218.869870] Hardware name: Intel Corporation Merrifield/BODEGA BAY,
    > BIOS 542 2015.01.21:18.19.48
    > [ 218.878681] Workqueue: kacpi_hotplug acpi_device_del_work_fn
    > [ 218.884380] RIP: 0010:0xffff8f8f06559dc0
    > [ 218.888328] Code: ff ff d2 2b 21 8c ff ff ff ff 08 00 00 00 00 00
    > 00 00 78 34 fa 02 8f 8f ff ff 00 00 00 00 00
    > 00 00 00 00 00 00 00 00 00 00 00 <72> 65 67 75 6c 61 74 6f 72 3a 72 65
    > 67 75 6c 61 74 6f 72 2e 30 2d
    > [ 218.907138] RSP: 0000:ffffad36c0043c90 EFLAGS: 00010246
    > [ 218.912387] RAX: ffff8f8f06559dc0 RBX: ffff8f8f062cbc00 RCX: ffff8f8f01239fc8
    > [ 218.919542] RDX: 000000002a3cccf8 RSI: 0000000000000001 RDI: ffff8f8f06559480
    > [ 218.926701] RBP: ffffffffc037e279 R08: 00000000d5832520 R09: 0000000000000001
    > [ 218.933856] R10: 0000000000000000 R11: 0000000000000001 R12: ffff8f8f062cbc00
    > [ 218.941010] R13: ffffffffc038e028 R14: ffffffff8c5e0b60 R15: 00000000fffffffd
    > [ 218.948166] FS: 0000000000000000(0000) GS:ffff8f8f3e200000(0000)
    > knlGS:0000000000000000
    > [ 218.956286] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    > [ 218.962053] CR2: ffff8f8f06559dc0 CR3: 0000000002ef4000 CR4: 00000000001006f0
    > [ 218.969208] Call Trace:
    > [ 218.971678] ? hd44780_common_clear_display+0x17/0x30 [hd44780_common]
    > [ 218.978252] ? charlcd_write_char+0x21a/0x810 [charlcd]
    > [ 218.983519] ? charlcd_puts+0x30/0x60 [charlcd]
    > [ 218.988083] ? charlcd_unregister+0x24/0x70 [charlcd]
    > [ 218.993167] ? hd44780_remove+0x1e/0x30 [hd44780]
    > [ 218.997901] ? platform_remove+0x1f/0x40
    > ...
    >
    > Just for your information and with hope that somebody may test and/or
    > reproduce this and fix it. Later on I might find time to bisect the
    > other issue I mentioned above.

    For time being confirmed the following:
    1. a2060f288e15 ("auxdisplay: Call charlcd_backlight in place") has a
    remove bug (above), while panel works
    2. 66ce7d5c1e12 ("auxdisplay: Use an enum for charlcd backlight on/off
    ops") everything works as expected

    So, the oops introduced in between those two.

    --
    With Best Regards,
    Andy Shevchenko

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