linux-kernel - [PATCH RFC] x86/earlyprintk: Don't fail the pciserial device with incorrect class code

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Date:   Thu, 27 Sep 2018 20:43:20 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        H Peter Anvin <hpa@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Stuart R . Anderson" <stuart.r.anderson@...el.com>,
        alan@...ux.intel.com, x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Feng Tang <feng.tang@...el.com>
Subject: [PATCH RFC] x86/earlyprintk: Don't fail the pciserial device with incorrect class code

"pciserial" earlyprintk helps much on many modern x86 platforms,
but unfortunately there are some platforms whose PCI UART devices
have wrong PCI class code, which will be blocked by current check.

So loose the class code check by giving a warning message instead.
This should be fine, as a developer who can give the accurate
BDF should know whether it's a usable UART device.

Signed-off-by: Feng Tang <feng.tang@...el.com>
---
 arch/x86/kernel/early_printk.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index 5e801c8..abe1d08 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -265,7 +265,8 @@ static __init void early_pci_serial_init(char *s)
 	if (((classcode >> 16 != PCI_CLASS_COMMUNICATION_MODEM) &&
 	     (classcode >> 16 != PCI_CLASS_COMMUNICATION_SERIAL)) ||
 	   (((classcode >> 8) & 0xff) != 0x02)) /* 16550 I/F at BAR0 */
-		return;
+		pr_warn("earlyprintk: classcode for pcidev %d:%d:%d shows it's not a UART like device, please check!\n",
+			bus, slot, func);
 
 	/*
 	 * Determine if it is IO or memory mapped
-- 
2.7.4