add Kconfig option

Author: jofrev

components/sdmmc/Kconfig

@@ -5,4 +5,21 @@ menu "SD Protocol Layer Configuration"
         help
             Enable SDIO support.
             Disabling this will skip SDIO-specific initialization steps
+    config SD_UNALIGNED_MULTI_BLOCK_RW_MAX_CHUNK_SIZE
+        int "The maximum size of the chunks a SDMMC read/write to/from an unaligned buffer will be split into"
+        range 1 99999
+        default 1
+        help
+            The maximum size in blocks of the chunks a SDMMC read/write with an unaligned buffer will be split into.
+            The SDMMC driver requires aligned buffers for DMA access. If unaligned buffers are passed, an aligned
+            temporary buffer must be allocated for the actual transfer.
+            This option defines the maximum size for the temporary buffer, which equals this option's value multiplied
+            with the block size (typically 512 Bytes). A value of 16 therefore leads to up to 8192 bytes being
+            allocated on the heap for each transfer. The allocated buffer will never be larger than the number of bytes
+            to transfer in total.
+            It also decides whether single (value == 1) or multi block read/write (value > 1) commands are used.
+            With the default value of 1 single-block read/write commands will be used with the allocated buffer size
+            matching the block size.
+            You should keep this option at 1 if your card or configuration doesn't support the read or write multiple
+            blocks commands (CMD18 & CMD25).
 endmenu

components/sdmmc/sdmmc_cmd.c

@@ -468,7 +468,7 @@ esp_err_t sdmmc_write_sectors(sdmmc_card_t* card, const void* src,
         // SDMMC peripheral needs DMA-capable buffers. Split the write into
         // separate (multi) block writes, if needed, and allocate a temporary
         // DMA-capable buffer.
-        size_t blocks_per_write = MIN(MAX_NUM_BLOCKS_PER_MULTI_BLOCK_RW, block_count);
+        size_t blocks_per_write = MIN(CONFIG_SD_UNALIGNED_MULTI_BLOCK_RW_MAX_CHUNK_SIZE, block_count);
         void *tmp_buf = NULL;
         size_t actual_size = 0;
         // We don't want to force the allocation into SPIRAM, the allocator
@@ -609,7 +609,7 @@ esp_err_t sdmmc_read_sectors(sdmmc_card_t* card, void* dst,
         // SDMMC peripheral needs DMA-capable buffers. Split the read into
         // separate (multi) block reads, if needed, and allocate a temporary
         // DMA-capable buffer.
-        size_t blocks_per_read = MIN(MAX_NUM_BLOCKS_PER_MULTI_BLOCK_RW, block_count);
+        size_t blocks_per_read = MIN(CONFIG_SD_UNALIGNED_MULTI_BLOCK_RW_MAX_CHUNK_SIZE, block_count);
         void *tmp_buf = NULL;
         size_t actual_size = 0;
         // We don't want to force the allocation into SPIRAM, the allocator