ARC updates for 3.20

Some fixes, nothing too exciting this time as well...
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Merge tag 'arc-3.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc

Pull ARC updates from Vineet Gupta:
 "Some fixes, nothing too exciting this time as well..."

* tag 'arc-3.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc:
  ARC: fix page address calculation if PAGE_OFFSET != LINUX_LINK_BASE
  ARC: Fix earlycon build breakage
  ARC: Dynamically determine BASE_BAUD from DeviceTree
  arc: Remove unused prepare_to_copy()
  ARC: use ACCESS_ONCE in cmpxchg loop
  ARC: add some more comments to ret_from_fork
  ARC: fix /proc/cpuinfo for offline cpus

arch/arc/include/asm/pgtable.h

@@ -257,7 +257,8 @@ static inline void pmd_set(pmd_t *pmdp, pte_t *ptep)
 #define pmd_clear(xp)			do { pmd_val(*(xp)) = 0; } while (0)
 
 #define pte_page(x) (mem_map + \
-		(unsigned long)(((pte_val(x) - PAGE_OFFSET) >> PAGE_SHIFT)))
+		(unsigned long)(((pte_val(x) - CONFIG_LINUX_LINK_BASE) >> \
+				PAGE_SHIFT)))
 
 #define mk_pte(page, pgprot)						\
 ({									\

arch/arc/include/asm/processor.h

@@ -56,9 +56,6 @@ unsigned long thread_saved_pc(struct task_struct *t);
 /* Free all resources held by a thread */
 #define release_thread(thread) do { } while (0)
 
-/* Prepare to copy thread state - unlazy all lazy status */
-#define prepare_to_copy(tsk)    do { } while (0)
-
 /*
  * A lot of busy-wait loops in SMP are based off of non-volatile data otherwise
  * get optimised away by gcc

arch/arc/include/asm/serial.h

@@ -10,26 +10,13 @@
 #define _ASM_ARC_SERIAL_H
 
 /*
- * early-8250 requires BASE_BAUD to be defined and includes this header.
- * We put in a typical value:
- * 	(core clk / 16) - i.e. UART samples 16 times per sec.
- * Athough in multi-platform-image this might not work, specially if the
- * clk driving the UART is different.
- * We can't use DeviceTree as this is typically for early serial.
+ * early 8250 (now earlycon) requires BASE_BAUD to be defined in this header.
+ * However to still determine it dynamically (for multi-platform images)
+ * we do this in a helper by parsing the FDT early
  */
 
-#include <asm/clk.h>
+extern unsigned int __init arc_early_base_baud(void);
 
-#define BASE_BAUD	(arc_get_core_freq() / 16)
-
-/*
- * This is definitely going to break early 8250 consoles on multi-platform
- * images but hey, it won't add any code complexity for a debug feature of
- * one broken driver.
- */
-#ifdef CONFIG_ARC_PLAT_TB10X
-#undef BASE_BAUD
-#define BASE_BAUD	(arc_get_core_freq() / 16 / 3)
-#endif
+#define BASE_BAUD	arc_early_base_baud()
 
 #endif /* _ASM_ARC_SERIAL_H */

arch/arc/kernel/devtree.c

@@ -17,6 +17,28 @@
 #include <asm/clk.h>
 #include <asm/mach_desc.h>
 
+#ifdef CONFIG_SERIAL_EARLYCON
+
+static unsigned int __initdata arc_base_baud;
+
+unsigned int __init arc_early_base_baud(void)
+{
+	return arc_base_baud/16;
+}
+
+static void __init arc_set_early_base_baud(unsigned long dt_root)
+{
+	unsigned int core_clk = arc_get_core_freq();
+
+	if (of_flat_dt_is_compatible(dt_root, "abilis,arc-tb10x"))
+		arc_base_baud = core_clk/3;
+	else
+		arc_base_baud = core_clk;
+}
+#else
+#define arc_set_early_base_baud(dt_root)
+#endif
+
 static const void * __init arch_get_next_mach(const char *const **match)
 {
 	static const struct machine_desc *mdesc = __arch_info_begin;
@@ -56,5 +78,7 @@ const struct machine_desc * __init setup_machine_fdt(void *dt)
 	if (clk)
 		arc_set_core_freq(of_read_ulong(clk, len/4));
 
+	arc_set_early_base_baud(dt_root);
+
 	return mdesc;
 }

arch/arc/kernel/entry.S

@@ -736,16 +736,20 @@ ENTRY(ret_from_fork)
 	; put last task in scheduler queue
 	bl   @schedule_tail
 
-	; If kernel thread, jump to its entry-point
 	ld   r9, [sp, PT_status32]
 	brne r9, 0, 1f
 
-	jl.d [r14]
-	mov  r0, r13		; arg to payload
+	jl.d [r14]		; kernel thread entry point
+	mov  r0, r13		; (see PF_KTHREAD block in copy_thread)
 
 1:
-	; special case of kernel_thread entry point returning back due to
-	; kernel_execve() - pretend return from syscall to ret to userland
+	; Return to user space
+	; 1. Any forked task (Reach here via BRne above)
+	; 2. First ever init task (Reach here via return from JL above)
+	;    This is the historic "kernel_execve" use-case, to return to init
+	;    user mode, in a round about way since that is always done from
+	;    a kernel thread which is executed via JL above but always returns
+	;    out whenever kernel_execve (now inline do_fork()) is involved
 	b    ret_from_exception
 END(ret_from_fork)
 

arch/arc/kernel/setup.c

@@ -412,6 +412,11 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 	char *str;
 	int cpu_id = ptr_to_cpu(v);
 
+	if (!cpu_online(cpu_id)) {
+		seq_printf(m, "processor [%d]\t: Offline\n", cpu_id);
+		goto done;
+	}
+
 	str = (char *)__get_free_page(GFP_TEMPORARY);
 	if (!str)
 		goto done;
@@ -429,7 +434,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 
 	free_page((unsigned long)str);
 done:
-	seq_printf(m, "\n\n");
+	seq_printf(m, "\n");
 
 	return 0;
 }

arch/arc/kernel/smp.c

@@ -221,7 +221,7 @@ static void ipi_send_msg_one(int cpu, enum ipi_msg_type msg)
 	 * and read back old value
 	 */
 	do {
-		new = old = *ipi_data_ptr;
+		new = old = ACCESS_ONCE(*ipi_data_ptr);
 		new |= 1U << msg;
 	} while (cmpxchg(ipi_data_ptr, old, new) != old);