linux-kernel - Re: [PATCH v1] nfc: pn544: Fix occasional HW initialization failure

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Date:   Wed, 19 Feb 2020 11:11:30 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     digetx@...il.com
Cc:     sameo@...ux.intel.com, david@...t.cz, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] nfc: pn544: Fix occasional HW initialization failure

From: Dmitry Osipenko <digetx@...il.com>
Date: Wed, 19 Feb 2020 18:01:22 +0300

> The PN544 driver checks the "enable" polarity during of driver's probe and
> it's doing that by turning ON and OFF NFC with different polarities until
> enabling succeeds. It takes some time for the hardware to power-down, and
> thus, to deassert the IRQ that is raised by turning ON the hardware.
> Since the delay after last power-down of the polarity-checking process is
> missed in the code, the interrupt may trigger immediately after installing
> the IRQ handler (right after the checking is done), which results in IRQ
> handler trying to touch the disabled HW and ends with marking NFC as
> 'DEAD' during of the driver's probe:
> 
>   pn544_hci_i2c 1-002a: NFC: nfc_en polarity : active high
>   pn544_hci_i2c 1-002a: NFC: invalid len byte
>   shdlc: llc_shdlc_recv_frame: NULL Frame -> link is dead
> 
> This patch fixes the occasional NFC initialization failure on Nexus 7
> device.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>

Applied and queued up for -stable, thanks.