[RFC PATCH 1/9] usb: xhci: Add missing cache flush in the scratchpad array initialization

[Nicolas Saenz Julienne]

Hi Sylwester, Marek

On Tue, 2020-04-21 at 18:50 +0200, Sylwester Nawrocki wrote:
> In current code there is no cache flush after initializing the scratchpad
> buffer array with the scratchpad buffer pointers. This leads to a failure
> of the "slot enable" command on the rpi4 board (Broadcom STB PCIe
> controller + VL805 USB hub) - the very first TRB transfer on the command
> ring fails and there is a timeout while waiting for the command completion
> event. After adding the missing cache flush everything seems to be working
> as expected.
> 
> Signed-off-by: Sylwester Nawrocki <s.nawrocki at samsung.com>
> Reviewed-by: Bin Meng <bmeng.cn at gmail.com>
> ---

I've been trying to get this working on my own and got stuck with this specific
issue. I'm glad you found a solution, it was driving me crazy.

Out of curiosity how did you found the solution?

>  drivers/usb/host/xhci-mem.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index 93450ee..729bdc3 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -393,6 +393,9 @@ static int xhci_scratchpad_alloc(struct xhci_ctrl *ctrl)
>  		scratchpad->sp_array[i] = cpu_to_le64(ptr);
>  	}
>  
> +	xhci_flush_cache((uintptr_t)scratchpad->sp_array,
> +			 sizeof(u64) * num_sp);
> +

Marek, souldn't running 'dcache off; icache off' be equivalent to this (which
didn't do the trick for me)? or am I missing somthing?

Regards,
Nicolas

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