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Date:   Mon, 20 Nov 2023 13:27:08 +0100
From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     Francesco Dolcini <francesco@dolcini.it>
Cc:     John Ogness <john.ogness@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-rt-users@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>,
        francesco.dolcini@toradex.com
Subject: Re: [ANNOUNCE] v6.6-rt13
Message-ID: <20231120122708.UxA5Wf4b@linutronix.de>
References: <20231108152329.NDcgOQAF@linutronix.de>
 <ZVJ0B9HYLTsLxxXw@francesco-nb.int.toradex.com>
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On 2023-11-13 20:07:51 [+0100], Francesco Dolcini wrote:
> Hello Sebastian, hello John
Hi,

> During our weekly CI tests of rt-devel branch we noticed that commit
> 78f4b59c6faa ("printk: Update the printk series.") breaks booting on
> multiple NXP i.MX platforms (arm and arm64), likely related to
> drivers/tty/serial/imx.c.
> 
> We are not planning any additional investigation at the moment and
> we have no debug outputs to share, just wanted to give you a head-up.

Thank you for the report.
As it turns out, the new bits never saw the lights of a 32bit machine.
The following hunk should fix it:

diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index a949d02fbd174..b6a8306bfda89 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -1477,7 +1477,10 @@ static inline u64 __ulseq_to_u64seq(u32 ulseq)
 	 * sequence. It needs to be expanded to 64bit. Get the first sequence
 	 * number from the ringbuffer and fold it.
 	 */
-	seq = rb_first_seq - ((u32)rb_first_seq - ulseq);
+	if (rb_first_seq == 0)
+		seq = ulseq;
+	else
+		seq = rb_first_seq - ((u32)rb_first_seq - ulseq);
 
 	return seq;
 }


> Francesco

Sebastian