Re: [PATCH 6/6 v2] block: Add n64 cart driver

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On Mon, Jan 04, 2021 at 07:56:11PM +0200, Lauri Kasanen wrote:
> +static blk_status_t get_seg(struct request *req)
> +{
> +	u32 bstart = blk_rq_pos(req) * 512;
> +	u32 len = blk_rq_cur_bytes(req);
> +	void *dst = bio_data(req->bio);
> +
> +	if (bstart + len > size)
> +		return BLK_STS_IOERR;
> +
> +	bstart += start;
> +
> +	while (len) {
> +		const u32 curlen = len < BUFSIZE ? len : BUFSIZE;
> +
> +		dma_cache_inv((unsigned long) buf, curlen);
> +
> +		n64cart_wait_dma();
> +
> +		barrier();
> +		n64cart_write_reg(PI_DRAM_REG, dma_addr);
> +		barrier();
> +		n64cart_write_reg(PI_CART_REG, (bstart | 0x10000000) & 0x1FFFFFFF);
> +		barrier();
> +		n64cart_write_reg(PI_WRITE_REG, curlen - 1);
> +		barrier();
> +
> +		n64cart_wait_dma();
> +
> +		memcpy(dst, buf, curlen);

Is there a reason for using a bounce buffer rather than reading directly
into the destination?



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