x86/earlyprintk: Add a force option for pciserial device

The "pciserial" earlyprintk variant helps much on many modern x86
platforms, but unfortunately there are still some platforms with PCI
UART devices which have the wrong PCI class code. In that case, the
current class code check does not allow for them to be used for logging.

Add a sub-option "force" which overrides the class code check and thus
the use of such device can be enforced.

 [ bp: massage formulations. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Stuart R . Anderson" <stuart.r.anderson@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: H Peter Anvin <hpa@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thymo van Beers <thymovanbeers@gmail.com>
Cc: alan@linux.intel.com
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/20181002164921.25833-1-feng.tang@intel.com

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 92eb1f42240d7168354dc7129898e2500ef95c1a..34e6800dea0eed64c30d97a205c8b86014f307d1 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1063,7 +1063,7 @@
                        earlyprintk=serial[,0x...[,baudrate]]
                        earlyprintk=ttySn[,baudrate]
                        earlyprintk=dbgp[debugController#]
-                       earlyprintk=pciserial,bus:device.function[,baudrate]
+                       earlyprintk=pciserial[,force],bus:device.function[,baudrate]
                        earlyprintk=xdbc[xhciController#]
 
                        earlyprintk is useful when the kernel crashes before
@@ -1095,6 +1095,10 @@
 
                        The sclp output can only be used on s390.
 
+                       The optional "force" to "pciserial" enables use of a
+                       PCI device even when its classcode is not of the
+                       UART class.
+
        edac_report=    [HW,EDAC] Control how to report EDAC event
                        Format: {"on" | "off" | "force"}
                        on: enable EDAC to report H/W event. May be overridden

diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index 5e801c8c8ce7cfaf191505fc9feaae5414f7270b..374a52fa529694f7399ad59e0b4ec2c1d598c636 100644 (file)
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -213,8 +213,9 @@ static unsigned int mem32_serial_in(unsigned long addr, int offset)
  * early_pci_serial_init()
  *
  * This function is invoked when the early_printk param starts with "pciserial"
- * The rest of the param should be ",B:D.F,baud" where B, D & F describe the
- * location of a PCI device that must be a UART device.
+ * The rest of the param should be "[force],B:D.F,baud", where B, D & F describe
+ * the location of a PCI device that must be a UART device. "force" is optional
+ * and overrides the use of an UART device with a wrong PCI class code.
  */
 static __init void early_pci_serial_init(char *s)
 {
@@ -224,17 +225,23 @@ static __init void early_pci_serial_init(char *s)
        u32 classcode, bar0;
        u16 cmdreg;
        char *e;
+       int force = 0;
 
-
-       /*
-        * First, part the param to get the BDF values
-        */
        if (*s == ',')
                ++s;
 
        if (*s == 0)
                return;
 
+       /* Force the use of an UART device with wrong class code */
+       if (!strncmp(s, "force,", 6)) {
+               force = 1;
+               s += 6;
+       }
+
+       /*
+        * Part the param to get the BDF values
+        */
        bus = (u8)simple_strtoul(s, &e, 16);
        s = e;
        if (*s != ':')
@@ -253,7 +260,7 @@ static __init void early_pci_serial_init(char *s)
                s++;
 
        /*
-        * Second, find the device from the BDF
+        * Find the device from the BDF
         */
        cmdreg = read_pci_config(bus, slot, func, PCI_COMMAND);
        classcode = read_pci_config(bus, slot, func, PCI_CLASS_REVISION);
@@ -264,8 +271,10 @@ 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;
+          (((classcode >> 8) & 0xff) != 0x02)) /* 16550 I/F at BAR0 */ {
+               if (!force)
+                       return;
+       }
 
        /*
         * Determine if it is IO or memory mapped
@@ -289,7 +298,7 @@ static __init void early_pci_serial_init(char *s)
        }
 
        /*
-        * Lastly, initialize the hardware
+        * Initialize the hardware
         */
        if (*s) {
                if (strcmp(s, "nocfg") == 0)