Jason McMullan mcmullan@netapp.com wrote:
This commit adds MTD support for the M25P80 (1Mx8) and the M25P40 (512kx8) SPI Flash components from ST Microelectronics.
Tested with the M25P40, but should work for the M25P80 according to the spec sheet.
Nice. I have a few minor comments below.
Could you add some information on how to obtain data sheets for these things? I had some difficulty finding it.
FWIW, I think it's here:
http://www.numonyx.com/en-US/MemoryProducts/NOR/Pages/M25PTechnicalDocuments...
+struct stmicro_spi_flash_params {
- uint8_t esig;
- /* Log2 of page size in power-of-two mode */
Do these chips support anything but power-of-two page sizes? I always thought that was an AT45 DataFlash peculiarity...
I can't find anything in the M25P80 indicating that the page size can be different from 256...
- uint8_t l2_page_size;
+/*
- Assemble the address part of a command for STMicro devices in
- non-power-of-two page size mode.
- */
This comment is misleading. The below code only works for power-of-two page sizes.
+static void stmicro_build_address(struct stmicro_spi_flash *stm, u8 *cmd, u32 offset) +{
- unsigned long page_addr;
- unsigned long byte_addr;
- unsigned long page_size;
- unsigned int page_shift;
- /*
* The "extra" space per page is the power-of-two page size* divided by 32.*/
This comment is misleading too. There's no "extra" space in the calculations below...
- page_shift = stm->params->l2_page_size;
- page_size = (1 << page_shift);
- page_addr = offset / page_size;
- byte_addr = offset % page_size;
...which means that you can make these operations cheaper by using shift and mask instead of divide and modulo. Though I suppose a clever compiler might figure that out on its own...
+static int stmicro_write(struct spi_flash *flash,
u32 offset, size_t len, const void *buf)+{
- struct stmicro_spi_flash *stm = to_stmicro_spi_flash(flash);
- unsigned long page_addr;
- unsigned long byte_addr;
- unsigned long page_size;
- unsigned int page_shift;
- size_t chunk_len;
- size_t actual;
- int ret;
- u8 cmd[4];
- page_shift = stm->params->l2_page_size;
- page_size = (1 << page_shift);
- page_addr = offset / page_size;
- byte_addr = offset % page_size;
Same thing here. Could you have a look at the disassembly to see if the compiler _is_ clever enough to optimize away the divide/modulo?
Haavard