[RFC v3 PATCH 1/7] ARM: add support for kernel mode NEON in atomic context

On 15 October 2013 19:26, Catalin Marinas [off-list ref] wrote:

On Sun, Oct 13, 2013 at 01:14:57PM +0100, Ard Biesheuvel wrote:

quoted

diff --git a/arch/arm/include/asm/neon.h b/arch/arm/include/asm/neon.h
index 8f730fe..800d85c 100644
--- a/arch/arm/include/asm/neon.h
+++ b/arch/arm/include/asm/neon.h

@@ -8,10 +8,30 @@
  * published by the Free Software Foundation.
  */

+#include <linux/types.h>
+#include <linux/hardirq.h>
+#include <asm/fpstate.h>
 #include <asm/hwcap.h>

 #define cpu_has_neon()               (!!(elf_hwcap & HWCAP_NEON))

+/*
+ * Avoid wasting stack space by making the size of the allocated area depend on
+ * whether we are currently running in process context. (If this is the case, we
+ * will use the normal preserve/restore mechanism, leaving the allocated stack
+ * space unused.)
+ */
+#define __QREG_SIZE(num)     \
+     ((!in_interrupt()) ? 0 : (num) > 16 ? 256 : 16 * (((num) + 1) & ~1U))
+
+#define DEFINE_NEON_REGSTACK_PARTIAL(v, num)         \
+     struct {                                        \
+             struct vfp_partial_state regs;          \
+             u8 qregs[__QREG_SIZE(num)];             \
+     } v

Oh, interesting gcc feature. What does it generate?

Well, it's not a feature particular to GCC, as far as I am aware. The
anonymous struct is just runtime variably sized depending on
in_interrupt() and the requested number of registers.

-- 
Ard.