Re: [PATCH] mmc: core Drop BLK_BOUNCE_HIGH

[Ulf Hansson]

On Thu, 25 Jan 2024 at 09:50, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
>
> The MMC core sets BLK_BOUNCE_HIGH for devices where dma_mask
> is unassigned.
>
> For the majority of MMC hosts this path is never taken: the
> OF core will unconditionally assign a 32-bit mask to any
> OF device, and most MMC hosts are probed from device tree,
> see drivers/of/platform.c:
>
> of_platform_device_create_pdata()
>         dev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
>         if (!dev->dev.dma_mask)
>                 dev->dev.dma_mask = &dev->dev.coherent_dma_mask;
>
> of_amba_device_create()
>         dev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
>         dev->dev.dma_mask = &dev->dev.coherent_dma_mask;
>
> MMC devices that are probed from ACPI or PCI will likewise
> have a proper dma_mask assigned.
>
> The only remaining devices that could have a blank dma_mask
> are platform devices instantiated from board files.
>
> These are mostly used on systems without CONFIG_HIGHMEM
> enabled which means the block layer will not bounce, and in
> the few cases where it is enabled it is not used anyway:
> for example some OMAP2 systems such as Nokia n800/n810 will
> create a platform_device and not assign a dma_mask, however
> they do not have any highmem, so no bouncing will happen
> anyway: the block core checks if max_low_pfn >= max_pfn
> and this will always be false.
>
> Should it turn out there is a platform_device with blank
> DMA mask actually using CONFIG_HIGHMEM somewhere out there
> we should set dma_mask for it, not do this trickery.
>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>

Applied for next, thanks!

Kind regards
Uffe


> ---
>  drivers/mmc/core/queue.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
> index a0a2412f62a7..316415588a77 100644
> --- a/drivers/mmc/core/queue.c
> +++ b/drivers/mmc/core/queue.c
> @@ -351,8 +351,6 @@ static void mmc_setup_queue(struct mmc_queue *mq, struct mmc_card *card)
>         if (mmc_can_erase(card))
>                 mmc_queue_setup_discard(mq->queue, card);
>
> -       if (!mmc_dev(host)->dma_mask || !*mmc_dev(host)->dma_mask)
> -               blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_HIGH);
>         blk_queue_max_hw_sectors(mq->queue,
>                 min(host->max_blk_count, host->max_req_size / 512));
>         if (host->can_dma_map_merge)
>
> ---
> base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
> change-id: 20240124-mmc-no-blk-bounce-high-d84e8898c707
>
> Best regards,
> --
> Linus Walleij <linus.walleij@xxxxxxxxxx>
>