Re: [PATCH] usb-storage: stop using block layer bounce buffers

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On Sun, 15 Apr 2018, Christoph Hellwig wrote:

> USB host controllers now must handle highmem, so we can get rid of bounce
> buffering highmem pages in the block layer.

Sorry, I don't quite understand what you are saying.  Do you mean that
all USB host controllers now magically _do_ handle highmem?  Or do you
mean that if they _don't_ handle highmem, we will not support them any
more?

Alan Stern

> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  drivers/usb/storage/scsiglue.c | 9 ---------
>  1 file changed, 9 deletions(-)
> 
> diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
> index c267f2812a04..4e453d9d45d5 100644
> --- a/drivers/usb/storage/scsiglue.c
> +++ b/drivers/usb/storage/scsiglue.c
> @@ -130,15 +130,6 @@ static int slave_configure(struct scsi_device *sdev)
>  		blk_queue_max_hw_sectors(sdev->request_queue, 2048);
>  	}
>  
> -	/*
> -	 * Some USB host controllers can't do DMA; they have to use PIO.
> -	 * They indicate this by setting their dma_mask to NULL.  For
> -	 * such controllers we need to make sure the block layer sets
> -	 * up bounce buffers in addressable memory.
> -	 */
> -	if (!us->pusb_dev->bus->controller->dma_mask)
> -		blk_queue_bounce_limit(sdev->request_queue, BLK_BOUNCE_HIGH);
> -
>  	/*
>  	 * We can't put these settings in slave_alloc() because that gets
>  	 * called before the device type is known.  Consequently these
> 




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