Re: [PATCH 4/7] usb-storage: reject probe of device one non-DMA HCDs when using highmem

[Sergey Shtylyov <s.shtylyov@omp.ru>]

On 5/2/25 9:49 AM, Christoph Hellwig wrote:

> usb-storage is the last user of the block layer bounce buffering now,
> and only uses it for HCDs that do not support DMA on highmem configs.
> 
> Remove this support and fail the probe so that the block layer bounce
> buffering can go away.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/usb/storage/usb.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
> index d36f3b6992bb..49bbfe4610d5 100644
> --- a/drivers/usb/storage/usb.c
> +++ b/drivers/usb/storage/usb.c
> @@ -1057,12 +1057,15 @@ int usb_stor_probe1(struct us_data **pus,
>  
>  	/*
>  	 * Some USB host controllers can't do DMA; they have to use PIO.
> -	 * For such controllers we need to make sure the block layer sets
> -	 * up bounce buffers in addressable memory.
> +	 * We can't support these controllers on highmem systems as the
> +	 * usb-storage code lacks the code to kmap or bounce buffer.
>  	 */
> -	if (!hcd_uses_dma(bus_to_hcd(us->pusb_dev->bus)) ||
> -	    bus_to_hcd(us->pusb_dev->bus)->localmem_pool)
> -		host->no_highmem = true;
> +	if (IS_ENABLED(CONFIG_HIGHMEM) &&
> +	    (!hcd_uses_dma(bus_to_hcd(us->pusb_dev->bus)) ||
> +	     bus_to_hcd(us->pusb_dev->bus)->localmem_pool)) {
> +		dev_warn(&intf->dev, "USB Mass Storage device not support on this HCD\n");

   Supported, perhaps?

[...]

MBR, Sergey