Re: [comments] MMC: Reliable write support.

[Arnd Bergmann <arnd@arndb.de>]

On Thursday 24 March 2011, Andrei Warkentin wrote:
> This is a request-for-comments patch. Please provide your feedback.
> 
> Allows reliable writes to be used for MMC writes. Reliable writes are used
> to service write REQ_FUA/REQ_META requests. Handles both the legacy and the enhanced
> reliable write support in MMC cards.
> 
> Beyond REQ_FUA/REQ_META, this was meant to be used by a following patch that aimed
> to reduce write amplification issues in cards employing a small (usually flash page-sized)
> buffer and a large (usually erase-block sized) buffer, at the expense of performance.

Looks good to me, but I don't really understand some of the block layer
specifics here. One question:

> +static int mmc_blk_issue_flush(struct mmc_queue *mq, struct request *req)
> +{
> +	struct mmc_blk_data *md = mq->data;
> +
> +	/*
> +	   No-op, only service this because we need REQ_FUA
> +	   for reliable writes.
> +	*/
> +	spin_lock_irq(&md->lock);
> +	__blk_end_request_all(req, 0);
> +	spin_unlock_irq(&md->lock);
> +
> +	return 1;
> +}

How does this work when you have a flush that does not directly follow
a REQ_FUA or REQ_META request? I would assume that we still need to
flush in some way, which you don't seem to do here.

	Arnd