This commit introduces two helper functions, `__memcpy_fromio` and
`__memcpy_toio`, to provide a robust mechanism for copying data between
standard memory and memory-mapped I/O (MMIO) space for the ARM
architecture.
These functions are designed to handle memory transfers safely,
accounting for potential address alignment issues to ensure correctness
and improve performance where possible. The implementation is specific
to ARM and uses relaxed I/O accessors.
__memcpy_fromio:
Copies a block of data from an I/O memory source to a destination in
standard ("real") memory. The implementation first handles any unaligned
bytes at the beginning of the source buffer individually using byte-wise
reads. It then copies the bulk of the data using 32-bit reads for
efficiency, and finally processes any remaining bytes at the end of the
buffer.
__memcpy_toio:
Copies a block of data from standard memory to a destination in I/O
memory space. It follows a similar strategy, handling any initial
unaligned portion of the destination buffer byte-by-byte before using
more efficient 32-bit writes for the main, aligned part of the transfer.
Any trailing bytes are also handled individually.
xen/include/xen/lib/arm/io.h
Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com>
---
Changes in v5:
- move memcpy_toio/fromio to the generic place
xen/include/xen/lib/arm/io.h | 15 +++++++
xen/lib/Makefile | 1 +
xen/lib/arm/Makefile | 1 +
xen/lib/arm/io.c | 80 ++++++++++++++++++++++++++++++++++++
4 files changed, 97 insertions(+)
create mode 100644 xen/include/xen/lib/arm/io.h
create mode 100644 xen/lib/arm/Makefile
create mode 100644 xen/lib/arm/io.c
diff --git a/xen/include/xen/lib/arm/io.h b/xen/include/xen/lib/arm/io.h
new file mode 100644
index 0000000000..86973660ba
--- /dev/null
+++ b/xen/include/xen/lib/arm/io.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _XEN_LIB_ARM_IO_H
+#define _XEN_LIB_ARM_IO_H
+
+#include <xen/types.h>
+
+/*
+ * Prototypes for I/O memory access functions.
+ */
+extern void __memcpy_fromio(void *to, const volatile void __iomem *from,
+ size_t count);
+extern void __memcpy_toio(volatile void __iomem *to, const void *from,
+ size_t count);
+
+#endif /* _XEN_LIB_ARM_IO_H */
diff --git a/xen/lib/Makefile b/xen/lib/Makefile
index 5ccb1e5241..efa8157a72 100644
--- a/xen/lib/Makefile
+++ b/xen/lib/Makefile
@@ -1,4 +1,5 @@
obj-$(CONFIG_X86) += x86/
+obj-$(CONFIG_ARM) += arm/
lib-y += bsearch.o
lib-y += ctors.o
diff --git a/xen/lib/arm/Makefile b/xen/lib/arm/Makefile
new file mode 100644
index 0000000000..87250b3822
--- /dev/null
+++ b/xen/lib/arm/Makefile
@@ -0,0 +1 @@
+obj-y += io.o
\ No newline at end of file
diff --git a/xen/lib/arm/io.c b/xen/lib/arm/io.c
new file mode 100644
index 0000000000..d267bd28e4
--- /dev/null
+++ b/xen/lib/arm/io.c
@@ -0,0 +1,80 @@
+#include <asm/io.h>
+#include <xen/lib/arm/io.h>
+
+/*
+ * memcpy_fromio - Copy data from IO memory space to "real" memory space.
+ * @to: Where to copy to
+ * @from: Where to copy from
+ * @count: The size of the area.
+ */
+void __memcpy_fromio(void *to, const volatile void __iomem *from,
+ size_t count)
+{
+ while ( count && !IS_ALIGNED((unsigned long)from, 4) )
+ {
+ *(u8 *)to = readb_relaxed(from);
+ from++;
+ to++;
+ count--;
+ }
+
+ while ( count >= 4 )
+ {
+ *(u32 *)to = readl_relaxed(from);
+ from += 4;
+ to += 4;
+ count -= 4;
+ }
+
+ while ( count )
+ {
+ *(u8 *)to = readb_relaxed(from);
+ from++;
+ to++;
+ count--;
+ }
+}
+
+/*
+ * memcpy_toio - Copy data from "real" memory space to IO memory space.
+ * @to: Where to copy to
+ * @from: Where to copy from
+ * @count: The size of the area.
+ */
+void __memcpy_toio(volatile void __iomem *to, const void *from,
+ size_t count)
+{
+ while ( count && !IS_ALIGNED((unsigned long)to, 4) )
+ {
+ writeb_relaxed(*(u8 *)from, to);
+ from++;
+ to++;
+ count--;
+ }
+
+ while ( count >= 4 )
+ {
+ writel_relaxed(*(u32 *)from, to);
+ from += 4;
+ to += 4;
+ count -= 4;
+ }
+
+ while ( count )
+ {
+ writeb_relaxed(*(u8 *)from, to);
+ from++;
+ to++;
+ count--;
+ }
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 8
+ * tab-width: 8
+ * indent-tabs-mode: t
+ * End:
+ */
--
2.34.1On Tue, 22 Jul 2025, Oleksii Moisieiev wrote:
> This commit introduces two helper functions, `__memcpy_fromio` and
> `__memcpy_toio`, to provide a robust mechanism for copying data between
> standard memory and memory-mapped I/O (MMIO) space for the ARM
> architecture.
>
> These functions are designed to handle memory transfers safely,
> accounting for potential address alignment issues to ensure correctness
> and improve performance where possible. The implementation is specific
> to ARM and uses relaxed I/O accessors.
>
> __memcpy_fromio:
> Copies a block of data from an I/O memory source to a destination in
> standard ("real") memory. The implementation first handles any unaligned
> bytes at the beginning of the source buffer individually using byte-wise
> reads. It then copies the bulk of the data using 32-bit reads for
> efficiency, and finally processes any remaining bytes at the end of the
> buffer.
>
> __memcpy_toio:
> Copies a block of data from standard memory to a destination in I/O
> memory space. It follows a similar strategy, handling any initial
> unaligned portion of the destination buffer byte-by-byte before using
> more efficient 32-bit writes for the main, aligned part of the transfer.
> Any trailing bytes are also handled individually.
> xen/include/xen/lib/arm/io.h
>
> Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@epam.com>
> ---
>
> Changes in v5:
> - move memcpy_toio/fromio to the generic place
>
> xen/include/xen/lib/arm/io.h | 15 +++++++
> xen/lib/Makefile | 1 +
> xen/lib/arm/Makefile | 1 +
> xen/lib/arm/io.c | 80 ++++++++++++++++++++++++++++++++++++
> 4 files changed, 97 insertions(+)
> create mode 100644 xen/include/xen/lib/arm/io.h
> create mode 100644 xen/lib/arm/Makefile
> create mode 100644 xen/lib/arm/io.c
>
> diff --git a/xen/include/xen/lib/arm/io.h b/xen/include/xen/lib/arm/io.h
> new file mode 100644
> index 0000000000..86973660ba
> --- /dev/null
> +++ b/xen/include/xen/lib/arm/io.h
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef _XEN_LIB_ARM_IO_H
> +#define _XEN_LIB_ARM_IO_H
> +
> +#include <xen/types.h>
> +
> +/*
> + * Prototypes for I/O memory access functions.
> + */
> +extern void __memcpy_fromio(void *to, const volatile void __iomem *from,
> + size_t count);
> +extern void __memcpy_toio(volatile void __iomem *to, const void *from,
> + size_t count);
> +
> +#endif /* _XEN_LIB_ARM_IO_H */
> diff --git a/xen/lib/Makefile b/xen/lib/Makefile
> index 5ccb1e5241..efa8157a72 100644
> --- a/xen/lib/Makefile
> +++ b/xen/lib/Makefile
> @@ -1,4 +1,5 @@
> obj-$(CONFIG_X86) += x86/
> +obj-$(CONFIG_ARM) += arm/
>
> lib-y += bsearch.o
> lib-y += ctors.o
> diff --git a/xen/lib/arm/Makefile b/xen/lib/arm/Makefile
> new file mode 100644
> index 0000000000..87250b3822
> --- /dev/null
> +++ b/xen/lib/arm/Makefile
> @@ -0,0 +1 @@
> +obj-y += io.o
> \ No newline at end of file
> diff --git a/xen/lib/arm/io.c b/xen/lib/arm/io.c
> new file mode 100644
> index 0000000000..d267bd28e4
> --- /dev/null
> +++ b/xen/lib/arm/io.c
> @@ -0,0 +1,80 @@
> +#include <asm/io.h>
> +#include <xen/lib/arm/io.h>
Please add the SPDX tag
> +/*
> + * memcpy_fromio - Copy data from IO memory space to "real" memory space.
> + * @to: Where to copy to
> + * @from: Where to copy from
> + * @count: The size of the area.
> + */
> +void __memcpy_fromio(void *to, const volatile void __iomem *from,
> + size_t count)
> +{
> + while ( count && !IS_ALIGNED((unsigned long)from, 4) )
> + {
> + *(u8 *)to = readb_relaxed(from);
> + from++;
> + to++;
> + count--;
> + }
> +
> + while ( count >= 4 )
> + {
> + *(u32 *)to = readl_relaxed(from);
> + from += 4;
> + to += 4;
> + count -= 4;
> + }
> +
> + while ( count )
> + {
> + *(u8 *)to = readb_relaxed(from);
> + from++;
> + to++;
> + count--;
> + }
> +}
> +
> +/*
> + * memcpy_toio - Copy data from "real" memory space to IO memory space.
> + * @to: Where to copy to
> + * @from: Where to copy from
> + * @count: The size of the area.
> + */
> +void __memcpy_toio(volatile void __iomem *to, const void *from,
> + size_t count)
> +{
> + while ( count && !IS_ALIGNED((unsigned long)to, 4) )
> + {
> + writeb_relaxed(*(u8 *)from, to);
> + from++;
> + to++;
> + count--;
> + }
> +
> + while ( count >= 4 )
> + {
> + writel_relaxed(*(u32 *)from, to);
> + from += 4;
> + to += 4;
> + count -= 4;
> + }
> +
> + while ( count )
> + {
> + writeb_relaxed(*(u8 *)from, to);
> + from++;
> + to++;
> + count--;
> + }
> +}
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 8
> + * tab-width: 8
> + * indent-tabs-mode: t
> + * End:
> + */
> --
> 2.34.1
>
On 22.07.2025 13:41, Oleksii Moisieiev wrote:
> This commit introduces two helper functions, `__memcpy_fromio` and
> `__memcpy_toio`, to provide a robust mechanism for copying data between
> standard memory and memory-mapped I/O (MMIO) space for the ARM
> architecture.
>
> These functions are designed to handle memory transfers safely,
> accounting for potential address alignment issues to ensure correctness
> and improve performance where possible. The implementation is specific
> to ARM and uses relaxed I/O accessors.
The implementation could be reused by any arch providing
{read,write}*_relaxed(), couldn't it?
> __memcpy_fromio:
> Copies a block of data from an I/O memory source to a destination in
> standard ("real") memory. The implementation first handles any unaligned
> bytes at the beginning of the source buffer individually using byte-wise
> reads. It then copies the bulk of the data using 32-bit reads for
> efficiency, and finally processes any remaining bytes at the end of the
> buffer.
>
> __memcpy_toio:
> Copies a block of data from standard memory to a destination in I/O
> memory space. It follows a similar strategy, handling any initial
> unaligned portion of the destination buffer byte-by-byte before using
> more efficient 32-bit writes for the main, aligned part of the transfer.
> Any trailing bytes are also handled individually.
> xen/include/xen/lib/arm/io.h
Why exactly do the functions need two leading underscores in their names?
> --- a/xen/lib/Makefile
> +++ b/xen/lib/Makefile
> @@ -1,4 +1,5 @@
> obj-$(CONFIG_X86) += x86/
> +obj-$(CONFIG_ARM) += arm/
Nit: Alphabetically sorted please.
> --- /dev/null
> +++ b/xen/lib/arm/Makefile
> @@ -0,0 +1 @@
> +obj-y += io.o
> \ No newline at end of file
Please make sure all files properly end in a newline.
> --- /dev/null
> +++ b/xen/lib/arm/io.c
> @@ -0,0 +1,80 @@
> +#include <asm/io.h>
> +#include <xen/lib/arm/io.h>
> +
> +/*
> + * memcpy_fromio - Copy data from IO memory space to "real" memory space.
> + * @to: Where to copy to
> + * @from: Where to copy from
> + * @count: The size of the area.
> + */
> +void __memcpy_fromio(void *to, const volatile void __iomem *from,
> + size_t count)
> +{
> + while ( count && !IS_ALIGNED((unsigned long)from, 4) )
> + {
> + *(u8 *)to = readb_relaxed(from);
No u<N> anymore in new code please; use uint<N>_t instead.
Further, what tells you that accessing a 16-bit register residing in MMIO
can legitimately be accessed using two 8-bit accesses?
> + from++;
> + to++;
> + count--;
> + }
> +
> + while ( count >= 4 )
> + {
> + *(u32 *)to = readl_relaxed(from);
> + from += 4;
> + to += 4;
> + count -= 4;
> + }
Not attempting 64-bit accesses on 64-bit arches will want an explanatory
comment, I think.
> + while ( count )
> + {
> + *(u8 *)to = readb_relaxed(from);
> + from++;
> + to++;
> + count--;
> + }
> +}
> +
> +/*
> + * memcpy_toio - Copy data from "real" memory space to IO memory space.
> + * @to: Where to copy to
> + * @from: Where to copy from
> + * @count: The size of the area.
> + */
> +void __memcpy_toio(volatile void __iomem *to, const void *from,
> + size_t count)
> +{
> + while ( count && !IS_ALIGNED((unsigned long)to, 4) )
> + {
> + writeb_relaxed(*(u8 *)from, to);
Please never cast away const-ness. This is a violation of some Misra rule,
iirc.
Jan
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