libhw_generic: Re-think duplex_iovec

8 files changed, 204 insertions, 56 deletions

diff --git a/libhw_cr/rp2040_hwspi.c b/libhw_cr/rp2040_hwspi.c
index 7b57792..d4adb11 100644
--- a/libhw_cr/rp2040_hwspi.c
+++ b/libhw_cr/rp2040_hwspi.c
@@ -185,23 +185,23 @@ static void rp2040_hwspi_readwritev(struct rp2040_hwspi *self, const struct dupl
 		if (!iov[i].iov_len)
 			continue;
 		tx_data_blocks[j]    = (typeof(tx_data_blocks[0])){
-			.read_addr   = iov[i].iov_write_src ?: &self->bogus_data,
+			.read_addr   = (iov[i].iov_write_from != IOVEC_DISCARD) ? iov[i].iov_write_from : &self->bogus_data,
 			.write_addr  = &spi_get_hw(self->inst)->dr,
 			.trans_count = iov[i].iov_len,
 			.ctrl        = (DMA_CTRL_ENABLE
 			                | DMA_CTRL_DATA_SIZE(DMA_SIZE_8)
-			                | (iov[i].iov_write_src ? DMA_CTRL_INCR_READ : 0)
+			                | ((iov[i].iov_write_from != IOVEC_DISCARD) ? DMA_CTRL_INCR_READ : 0)
 			                | DMA_CTRL_CHAIN_TO(self->dma_tx_ctrl)
 			                | DMA_CTRL_TREQ_SEL(SPI_DREQ_NUM(self->inst, true))
 			                | DMA_CTRL_IRQ_QUIET),
 		};
 		rx_data_blocks[j]    = (typeof(rx_data_blocks[0])){
 			.read_addr   = &spi_get_hw(self->inst)->dr,
-			.write_addr  = iov[i].iov_read_dst ?: &bogus_rx_dst,
+			.write_addr  = (iov[i].iov_read_to != IOVEC_DISCARD) ? iov[i].iov_read_to : &bogus_rx_dst,
 			.trans_count = iov[i].iov_len,
 			.ctrl        = (DMA_CTRL_ENABLE
 			                | DMA_CTRL_DATA_SIZE(DMA_SIZE_8)
-			                | (iov[i].iov_read_dst ? DMA_CTRL_INCR_WRITE : 0)
+			                | ((iov[i].iov_read_to != IOVEC_DISCARD) ? DMA_CTRL_INCR_WRITE : 0)
 			                | DMA_CTRL_CHAIN_TO(self->dma_rx_ctrl)
 			                | DMA_CTRL_TREQ_SEL(SPI_DREQ_NUM(self->inst, false))
 			                | DMA_CTRL_IRQ_QUIET),
diff --git a/libhw_cr/rp2040_include/libhw/rp2040_hwspi.h b/libhw_cr/rp2040_include/libhw/rp2040_hwspi.h
index eb54cdc..9d99f7b 100644
--- a/libhw_cr/rp2040_include/libhw/rp2040_hwspi.h
+++ b/libhw_cr/rp2040_include/libhw/rp2040_hwspi.h
@@ -48,7 +48,7 @@ LO_IMPLEMENTATION_H(spi, struct rp2040_hwspi, rp2040_hwspi)
  * @param mode        : enum spi_mode              : the SPI mode; SPI_MODE_{0..3}
  * @param baudrate_hz : uint                       : baudrate in Hz
  * @param min_delay_ns: uint64_t                   : minimum time for pin_cs to be high between messages
- * @param bogus_data  : uint8_t                    : bogus data to write when .iov_write_src is NULL
+ * @param bogus_data  : uint8_t                    : bogus data to write when .iov_write_from is IOVEC_DISCARD
  * @param pin_miso    : uint                       : pin number; 0, 4, 16, or 20 for _HWSPI_0; 8, 12, 24, or 28 for _HWSPI_1
  * @param pin_mosi    : uint                       : pin number; 3, 7, 19, or 23 for _HWSPI_0; 11, 15, or 27 for _HWSPI_1
  * @param pin_clk     : uint                       : pin number; 2, 6, 18, or 22 for _HWSPI_0; 10, 14, or 26 for _HWSPI_1
diff --git a/libhw_cr/w5500_ll.h b/libhw_cr/w5500_ll.h
index 8f5f9ec..2506cd2 100644
--- a/libhw_cr/w5500_ll.h
+++ b/libhw_cr/w5500_ll.h
@@ -93,39 +93,15 @@ w5500ll_writev(
 		(uint8_t)(addr & 0xFF),
 		(block & CTL_MASK_BLOCK) | CTL_W | CTL_OM_VDM,
 	};
-	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*(iovcnt+1));
+	int inner_cnt = 1+io_slice_cnt(iov, iovcnt, skip, max);
+	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*inner_cnt);
 	inner[0] = (struct duplex_iovec){
-		.iov_read_dst  = NULL,
-		.iov_write_src = header,
-		.iov_len       = sizeof(header),
+		.iov_read_to    = IOVEC_DISCARD,
+		.iov_write_from = header,
+		.iov_len        = sizeof(header),
 	};
-	int j = 1;
-	size_t skipped = 0, done = 0;
-	for (int i = 0; i < iovcnt && (max == 0 || done < max); i++) {
-		if (skipped < skip) {
-			if (skip - skipped >= iov[i].iov_len) {
-				skipped += iov[i].iov_len;
-				continue;
-			}
-			inner[j] = (struct duplex_iovec){
-				.iov_read_dst  = NULL,
-				.iov_write_src = iov[i].iov_base+(skip-skipped),
-				.iov_len       = iov[i].iov_len-(skip-skipped),
-			};
-			skipped = skip;
-		} else {
-			inner[j] = (struct duplex_iovec){
-				.iov_read_dst  = NULL,
-				.iov_write_src = iov[i].iov_base,
-				.iov_len       = iov[i].iov_len,
-			};
-		}
-		done += inner[j].iov_len;
-		if (max > 0 && done > max)
-			inner[j].iov_len -= done - max;
-		j++;
-	};
-	LO_CALL(spidev, readwritev, inner, j);
+	io_slice_wr_to_duplex(&inner[1], iov, iovcnt, skip, max);
+	LO_CALL(spidev, readwritev, inner, inner_cnt);
 }
 
 static inline void
@@ -154,26 +130,15 @@ w5500ll_readv(
 		(uint8_t)(addr & 0xFF),
 		(block & CTL_MASK_BLOCK) | CTL_R | CTL_OM_VDM,
 	};
-	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*(iovcnt+1));
+	int inner_cnt = 1+io_slice_cnt(iov, iovcnt, 0, max);
+	struct duplex_iovec *inner = alloca(sizeof(struct duplex_iovec)*inner_cnt);
 	inner[0] = (struct duplex_iovec){
-		.iov_read_dst  = NULL,
-		.iov_write_src = header,
-		.iov_len       = sizeof(header),
-	};
-	int j = 1;
-	size_t done = 0;
-	for (int i = 0; i < iovcnt && (max == 0 || done < max); i++) {
-		inner[j] = (struct duplex_iovec){
-			.iov_read_dst  = iov[i].iov_base,
-			.iov_write_src = NULL,
-			.iov_len       = iov[i].iov_len,
-		};
-		done += inner[j].iov_len;
-		if (max > 0 && done > max)
-			inner[j].iov_len -= done - max;
-		j++;
+		.iov_read_to    = IOVEC_DISCARD,
+		.iov_write_from = header,
+		.iov_len        = sizeof(header),
 	};
-	LO_CALL(spidev, readwritev, inner, j);
+	io_slice_rd_to_duplex(&inner[1], iov, iovcnt, 0, max);
+	LO_CALL(spidev, readwritev, inner, inner_cnt);
 }
 
 /* Common chip-wide registers.  ***********************************************/
diff --git a/libhw_generic/CMakeLists.txt b/libhw_generic/CMakeLists.txt
index b1632aa..5a6014b 100644
--- a/libhw_generic/CMakeLists.txt
+++ b/libhw_generic/CMakeLists.txt
@@ -12,5 +12,8 @@ target_link_libraries(libhw_generic INTERFACE
 
 target_sources(libhw_generic INTERFACE
 	alarmclock.c
+	io.c
 	net.c
 )
+
+add_lib_test(libhw_generic test_io)
diff --git a/libhw_generic/include/libhw/generic/io.h b/libhw_generic/include/libhw/generic/io.h
index a7f7378..7825c9f 100644
--- a/libhw_generic/include/libhw/generic/io.h
+++ b/libhw_generic/include/libhw/generic/io.h
@@ -8,6 +8,7 @@
 #define _LIBHW_GENERIC_IO_H_
 
 #include <stddef.h>    /* for size_t */
+#include <stdint.h>    /* for uintptr_t */
 #include <sys/types.h> /* for ssize_t */
 
 #include <libobj/obj.h>
@@ -23,12 +24,35 @@ struct iovec {
 };
 #endif
 
+#define IOVEC_DISCARD ((void*)(~((uintptr_t)0)))
+
 struct duplex_iovec {
-	void    *iov_read_dst;
-	void    *iov_write_src;
+	/**
+	 * NULL is a valid pointer value in iov_read_to and
+	 * iov_write_from.  To skip a read or write, use the special
+	 * value IOVEC_DISCARD.
+	 */
+	void    *iov_read_to;
+	void    *iov_write_from;
 	size_t   iov_len;
 };
 
+/* utilities ******************************************************************/
+
+/* slice iovec lists */
+int  io_slice_cnt       (                          const struct        iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+void io_slice           (struct        iovec *dst, const struct        iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+int  io_duplex_slice_cnt(                          const struct duplex_iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+void io_duplex_slice    (struct duplex_iovec *dst, const struct duplex_iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+
+/* convert iovec lists */
+void io_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt);
+void io_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt);
+
+/* slice and convert in one go */
+void io_slice_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+void io_slice_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_start, size_t byte_max_cnt);
+
 /* basic interfaces ***********************************************************/
 
 /**
diff --git a/libhw_generic/io.c b/libhw_generic/io.c
new file mode 100644
index 0000000..4ebff10
--- /dev/null
+++ b/libhw_generic/io.c
@@ -0,0 +1,98 @@
+/* libhw_generic/io.c - Utilities for device-independent I/O definitions
+ *
+ * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <libmisc/assert.h>
+
+#include <libhw/generic/io.h>
+
+#define IOV_ITER(ACTION)                                                \
+	assert(src_cnt >= 0);                                           \
+	assert(src_cnt == 0 || src);                                    \
+                                                                        \
+	const size_t byte_end = byte_beg + byte_max_cnt;                \
+	int j = 0;                                                      \
+	size_t byte_pos = 0;                                            \
+	for (int i = 0;                                                 \
+	     i < src_cnt && (byte_max_cnt == 0 || byte_pos < byte_end); \
+	     i++) {                                                     \
+		size_t off = 0, len;                                    \
+		if (byte_pos < byte_beg) {                              \
+			if (byte_beg - byte_pos >= src[i].iov_len) {    \
+				byte_pos += src[i].iov_len;             \
+				continue;                               \
+			}                                               \
+			off = byte_beg-byte_pos;                        \
+			len = src[i].iov_len-off;                       \
+			byte_pos = byte_beg;                            \
+		} else {                                                \
+			len = src[i].iov_len;                           \
+		}                                                       \
+		if (byte_max_cnt && byte_end - byte_pos < len)          \
+			len = byte_end - byte_pos;                      \
+		do { ACTION } while (0);                                \
+		byte_pos += len;                                        \
+		j++;                                                    \
+	}
+
+int io_slice_cnt(const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	IOV_ITER();
+	return j;
+}
+
+int io_duplex_slice_cnt(const struct duplex_iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	IOV_ITER();
+	return j;
+}
+
+void io_slice(struct iovec *dst, const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct iovec){
+			.iov_base = src[i].iov_base+off,
+			.iov_len  = len,
+		});
+	);
+}
+void io_slice_duplex(struct duplex_iovec *dst, const struct duplex_iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct duplex_iovec){
+			.iov_read_to    = src[i].iov_read_to+off,
+			.iov_write_from = src[i].iov_write_from+off,
+			.iov_len        = len,
+		});
+	);
+}
+
+void io_slice_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct duplex_iovec){
+			.iov_read_to    = src[i].iov_base+off,
+			.iov_write_from = IOVEC_DISCARD,
+			.iov_len        = len,
+		});
+	);
+}
+
+void io_slice_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int src_cnt, size_t byte_beg, size_t byte_max_cnt) {
+	assert(src_cnt == 0 || dst);
+	IOV_ITER(
+		dst[j] = ((struct duplex_iovec){
+			.iov_read_to    = IOVEC_DISCARD,
+			.iov_write_from = src[i].iov_base+off,
+			.iov_len        = len,
+		});
+	);
+}
+
+void io_rd_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt) {
+	io_slice_rd_to_duplex(dst, src, iovcnt, 0, 0);
+}
+
+void io_wr_to_duplex(struct duplex_iovec *dst, const struct iovec *src, int iovcnt) {
+	io_slice_wr_to_duplex(dst, src, iovcnt, 0, 0);
+}
diff --git a/libhw_generic/tests/test.h b/libhw_generic/tests/test.h
new file mode 120000
index 0000000..2fb1bd5
--- /dev/null
+++ b/libhw_generic/tests/test.h
@@ -0,0 +1 @@
+../../libmisc/tests/test.h
\ No newline at end of file
diff --git a/libhw_generic/tests/test_io.c b/libhw_generic/tests/test_io.c
new file mode 100644
index 0000000..0d6df11
--- /dev/null
+++ b/libhw_generic/tests/test_io.c
@@ -0,0 +1,57 @@
+/* libhw_generic/tests/test_io.c - Tests for <libmisc/io.h>
+ *
+ * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <string.h>
+
+#include <libhw/generic/io.h>
+
+#include "test.h"
+
+int main() {
+	char data[] = "abcdefghijklmnopqrstuvwxyz";
+	struct iovec src[] = {
+		{.iov_base = &data[1], .iov_len=3}, /* "bcd" */
+		{.iov_base = &data[20], .iov_len=4}, /* "uvwx" */
+	};
+	const int src_cnt = sizeof(src)/sizeof(src[0]);
+
+	struct duplex_iovec dst[2];
+
+#define TC(start, max, ...) do {                                                                 \
+		char *exp[] = {__VA_ARGS__};                                                     \
+		int exp_cnt = sizeof(exp)/sizeof(exp[0]);                                        \
+		int act_cnt = io_slice_cnt(src, src_cnt, start, max);                            \
+		test_assert(act_cnt == exp_cnt);                                                 \
+		memset(dst, 0, sizeof(dst));                                                     \
+		io_slice_wr_to_duplex(dst, src, src_cnt, start, max);                            \
+		for (int i = 0; i < act_cnt; i++) {                                              \
+			test_assert(dst[i].iov_read_to == IOVEC_DISCARD);                        \
+			test_assert(dst[i].iov_write_from != IOVEC_DISCARD);                     \
+			test_assert(dst[i].iov_len == strlen(exp[i]));                           \
+			test_assert(memcmp(dst[i].iov_write_from, exp[i], dst[i].iov_len) == 0); \
+		}                                                                                \
+	} while (0)
+
+	TC(0, 0, /* => */ "bcd", "uvwx");
+	TC(1, 0, /* => */ "cd", "uvwx");
+	TC(2, 0, /* => */ "d", "uvwx");
+	TC(3, 0, /* => */ "uvwx");
+	TC(4, 0, /* => */ "vwx");
+	TC(5, 0, /* => */ "wx");
+	TC(6, 0, /* => */ "x");
+	TC(7, 0, /* => */ );
+
+	TC(0, 2, /* => */ "bc");
+	TC(1, 2, /* => */ "cd");
+	TC(2, 2, /* => */ "d", "u");
+	TC(3, 2, /* => */ "uv");
+	TC(4, 2, /* => */ "vw");
+	TC(5, 2, /* => */ "wx");
+	TC(6, 2, /* => */ "x");
+	TC(7, 2, /* => */ );
+
+	return 0;
+}