Re: [PATCH 4.19.y-cip 6/7] spi: spi-mem: Add a new API to support direct mapping


Pavel Machek
 

Hi!

commit aa167f3fed0c37e0e4c707d4331d827661f46644 upstream.

Most modern SPI controllers can directly map a SPI memory (or a portion
of the SPI memory) in the CPU address space. Most of the time this
brings significant performance improvements as it automates the whole
process of sending SPI memory operations every time a new region is
accessed.

This new API allows SPI memory drivers to create direct mappings and
then use them to access the memory instead of using
spi_mem_exec_op().
+ * Return: the amount of data read from the memory device or a negative error
+ * code. Note that the returned size might be smaller than @len, and the caller
+ * is responsible for calling spi_mem_dirmap_read() again when that happens.
+ */
+ssize_t spi_mem_dirmap_read(struct spi_mem_dirmap_desc *desc,
+ u64 offs, size_t len, void *buf)
+{
+ struct spi_controller *ctlr = desc->mem->spi->controller;
+ ssize_t ret;
+
+ if (desc->info.op_tmpl.data.dir != SPI_MEM_DATA_IN)
+ return -EINVAL;
+
+ if (!len)
+ return 0;
+
+ if (desc->nodirmap) {
+ ret = spi_mem_no_dirmap_read(desc, offs, len, buf);
I'd do return ... here.

+ } else if (ctlr->mem_ops && ctlr->mem_ops->dirmap_read) {
+ ret = spi_mem_access_start(desc->mem);
+ if (ret)
+ return ret;
+
+ ret = ctlr->mem_ops->dirmap_read(desc, offs, len, buf);
+
+ spi_mem_access_end(desc->mem);
and here.

+ } else {
+ ret = -ENOTSUPP;
+ }
To help with if/else nesting. spi_mem_dirmap_write could use same
treatment.

Best regards,
Pavel

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