Re: [PATCH] mmc: mmci: Support non-power-of-two block sizes for ux500v2 variant

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Fri, Oct 12, 2012 at 04:02:02PM +0200, Ulf Hansson wrote:
>  /*
> + * Validate mmc prerequisites
> + */
> +static int mmci_validate_data(struct mmci_host *host,
> +			      struct mmc_data *data)
> +{
> +	if (!data)
> +		return 0;
> +
> +	if (!host->variant->non_power_of_2_blksize &&
> +	    !is_power_of_2(data->blksz)) {
> +		dev_err(mmc_dev(host->mmc),
> +			"unsupported block size (%d bytes)\n", data->blksz);
> +		return -EINVAL;
> +	}
> +
> +	if (data->sg->offset & 3) {
> +		dev_err(mmc_dev(host->mmc),
> +			"unsupported alginment (0x%x)\n", data->sg->offset);
> +		return -EINVAL;
> +	}

Why?  What's the reasoning behind this suddenly introduced restriction?
readsl()/writesl() copes just fine with non-aligned pointers.  It may be
that your DMA engine can not, but that's no business interfering with
non-DMA transfers, and no reason to fail such transfers.

If your DMA engine can't do that then its your DMA engine code which
should refuse to prepare the transfer.

Yes, that means problems with the way things are ordered - or it needs a
proper API where DMA engine can export these kinds of properties.