[coreboot-gerrit] Change in coreboot[master]: soc/mediatek/mt8192: Add SPI flash controller DMA read function

[Hung-Te Lin (Code Review)]

Hung-Te Lin has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/44851 )

Change subject: soc/mediatek/mt8192: Add SPI flash controller DMA read function
......................................................................

Patch Set 1:

(1 comment)

Changing from PIO+DMA (boot time: 879,067) to full-DMA (871,016) saved 8051us ~ 8ms. Please replace the PIO+DMA with my version (full DMA).

https://review.coreboot.org/c/coreboot/+/44851/1/src/soc/mediatek/mt8192/fla... 
File src/soc/mediatek/mt8192/flash_controller.c:

https://review.coreboot.org/c/coreboot/+/44851/1/src/soc/mediatek/mt8192/fla... 
PS1, Line 142: 	size_t done = 0;
             : 	uintptr_t dma_buf = (uintptr_t)_dma_coherent;
             : 	size_t dma_buf_len = REGION_SIZE(dma_coherent);
             : 	u32 next;
             : 
             : 	if (!IS_ALIGNED((uintptr_t)addr, SFLASH_DMA_ALIGN)) {
             : 		next = MIN(ALIGN_UP((uintptr_t)addr, SFLASH_DMA_ALIGN) -
             : 			   (uintptr_t)addr, len);
             : 		if (pio_read(addr, buf, next))
             : 			return -1;
             : 		done += next;
             : 	}
             : 
             : 	while (len - done >= SFLASH_DMA_ALIGN) {
             : 		next = MIN(dma_buf_len, ALIGN_DOWN(len - done,
             : 			   SFLASH_DMA_ALIGN));
             : 		if (dma_read(addr + done, buf + done, next, dma_buf,
             : 			     dma_buf_len))
             : 			return -1;
             : 		done += next;
             : 	}
             : 	next = len - done;
             : 	if (next > 0 && pio_read(addr + done, buf + done, next))
             : 		return -1;
> can we replace this by purely DMA calls, eg: […]

I tested and this works well:

static int nor_read(const struct spi_flash *flash, u32 addr, size_t len,
                     void *buf)
 {
        uintptr_t dma_buf = (uintptr_t)_dma_coherent;
        size_t dma_buf_len = REGION_SIZE(dma_coherent);

setbits8(&mt8192_nor->read_dual, SFLASH_READ_DUAL_EN);
        write8(&mt8192_nor->prgdata[3], SFLASH_1_1_2_READ);

u32 start = ALIGN_DOWN(addr, SFLASH_DMA_ALIGN);
        u32 skip = addr - start;
        u32 total = ALIGN_UP(skip + len, SFLASH_DMA_ALIGN);
        u32 drop = total - skip - len;
        u32 done, read_len, copy_len;
        uint8_t *dest = (uint8_t *)buf;

/* DMA: start [ skip | len | drop ]=total end */
        for (done = 0; done < total; dest += copy_len) {
                read_len = MIN(dma_buf_len, total - done);
                if (dma_read(start + done, dma_buf, read_len, dma_buf_len))
                        return -1;

done += read_len;

// decide the range to copy into buffer
                if (done == total)
                        read_len -= drop;  /* Only drop in last iteration */

copy_len = read_len - skip;
                memcpy(dest, (uint8_t *)dma_buf + skip, copy_len);

if (skip)
                        skip = 0;  /* Only apply skip in first iteration. */
        }

return 0;
 }