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Re: [XEN v2 11/12] xen/Arm: GICv3: Define macros to read/write 64 bit



Hi,

On 01/11/2022 07:08, Xenia Ragiadakou wrote:
On 10/31/22 17:13, Ayan Kumar Halder wrote:
Defined readq_relaxed()/writeq_relaxed() to read and write 64 bit regs.
This uses ldrd/strd instructions.

Signed-off-by: Ayan Kumar Halder <ayankuma@xxxxxxx>
---

Changes from :-
v1 - 1. Use ldrd/strd for readq_relaxed()/writeq_relaxed().
2. No need to use le64_to_cpu() as the returned byte order is already in cpu
endianess.

  xen/arch/arm/include/asm/arm32/io.h | 21 +++++++++++++++++++++
  1 file changed, 21 insertions(+)

diff --git a/xen/arch/arm/include/asm/arm32/io.h b/xen/arch/arm/include/asm/arm32/io.h
index 73a879e9fb..d9d19ad764 100644
--- a/xen/arch/arm/include/asm/arm32/io.h
+++ b/xen/arch/arm/include/asm/arm32/io.h
@@ -72,6 +72,22 @@ static inline u32 __raw_readl(const volatile void __iomem *addr)
          return val;
  }
+static inline u64 __raw_readq(const volatile void __iomem *addr)
+{
+        u64 val;
+        asm volatile("ldrd %Q1, %R1, %0"
+                     : "+Qo" (*(volatile u64 __force *)addr),
+                       "=r" (val));
+        return val;
+}
+
+static inline void __raw_writeq(u64 val, const volatile void __iomem *addr)
+{
+    asm volatile("strd %Q1, %R1, %0"
+                 : "+Q" (*(volatile u64 __force *)addr)
+                 : "r" (val));
+}
+
  #define __iormb()               rmb()
  #define __iowmb()               wmb()
@@ -80,17 +96,22 @@ static inline u32 __raw_readl(const volatile void __iomem *addr)
                                          __raw_readw(c)); __r; })
  #define readl_relaxed(c) ({ u32 __r = le32_to_cpu((__force __le32) \
                                          __raw_readl(c)); __r; })
+#define readq_relaxed(c) ({ u64 __r = le64_to_cpu((__force __le64) \
+                                        __raw_readq(c)); __r; })
  #define writeb_relaxed(v,c)     __raw_writeb(v,c)
  #define writew_relaxed(v,c)     __raw_writew((__force u16) cpu_to_le16(v),c)   #define writel_relaxed(v,c)     __raw_writel((__force u32) cpu_to_le32(v),c) +#define writeq_relaxed(v,c)     __raw_writeq((__force u64) cpu_to_le64(v),c)   #define readb(c)                ({ u8  __v = readb_relaxed(c); __iormb(); __v; })   #define readw(c)                ({ u16 __v = readw_relaxed(c); __iormb(); __v; })   #define readl(c)                ({ u32 __v = readl_relaxed(c); __iormb(); __v; }) +#define readq(c)                ({ u64 __v = readq_relaxed(c); __iormb(); __v; })
  #define writeb(v,c)             ({ __iowmb(); writeb_relaxed(v,c); })
  #define writew(v,c)             ({ __iowmb(); writew_relaxed(v,c); })
  #define writel(v,c)             ({ __iowmb(); writel_relaxed(v,c); })
+#define writeq(v,c)             ({ __iowmb(); writeq_relaxed(v,c); })
  #endif /* _ARM_ARM32_IO_H */

AFAIU, ldrd/strd accesses to MMIO are not guaranteed to be 64-bit single-copy atomic. So, as Julien suggested, you still need to use a different name to reflect this. Also, having nested virtualization in mind, since these instructions can't be virtualized, maybe it would be better to avoid using them for MMIO accesses.

+1. The previous version was actually using 32-bit access and it is not clear to me why the new version is using 64-bit access.

Cheers,

--
Julien Grall



 


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