Re: [PATCH v2 5/9] mmc: mvsdio: Use sg_miter for PIO

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On Sat, 27 Jan 2024, Linus Walleij wrote:

> Use the scatterlist memory iterator instead of just
> dereferencing virtual memory using sg_virt().
> This make highmem references work properly.
> 
> This driver also has a bug in the PIO sglist handling that
> is fixed as part of the patch: it does not travers the
> list of scatterbuffers: it will just process the first
> item in the list. This is fixed by augmenting the logic
> such that we do not process more than one sgitem
> per IRQ instead of counting down potentially the whole
> length of the request.
> 
> We can suspect that the PIO path is quite untested.

It was tested for sure ... at least by myself ... some 17 years ago !

> Suggested-by: Christoph Hellwig <hch@xxxxxx>
> Link: https://lore.kernel.org/linux-mmc/20240122073423.GA25859@xxxxxx/
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

[...]

>  		if (!nodma)
> -			dev_dbg(host->dev, "fallback to PIO for data at 0x%p size %d\n",
> -				host->pio_ptr, host->pio_size);
> +			dev_dbg(host->dev, "fallback to PIO for data\n");

Given this message is about telling you why PIO is used despite not 
having asked for it, I think it would be nicer to preserve the 
equivalent info responsible for this infliction i.e. data->sg->offset 
and data->blksz.

The rest looks sane to me ( ... I think).


Nicolas




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