[PATCH] usb: ehci: Fix "EHCI timed out on TD - token=XXXX" error on ehci-hcd

[Marek Vasut]

On 2/26/20 12:29 PM, Lukasz Majewski wrote:
> This patch aims to improve robustness of 'usb' command operation on the
> ehci-hcd IP block as it ports to contemporary U-Boot the patch described
> and provided in [1] (originally applicable to U-Boot 2016.05).
> 
> According to the fix author - "rayvt" (from [1]):

[...]

> diff --git a/common/usb_storage.c b/common/usb_storage.c
> index 097b6729c1..48c8c2ae64 100644
> --- a/common/usb_storage.c
> +++ b/common/usb_storage.c
> @@ -111,6 +111,18 @@ int usb_stor_get_info(struct usb_device *dev, struct us_data *us,
>  		      struct blk_desc *dev_desc);
>  int usb_storage_probe(struct usb_device *dev, unsigned int ifnum,
>  		      struct us_data *ss);
> +
> +#ifdef CONFIG_USB_EHCI_HCD
> +	/*
> +	 * The U-Boot EHCI driver can handle any transfer length as long as
> +	 * there is enough free heap space left, but the SCSI READ(10) and
> +	 * WRITE(10) commands are limited to 65535 blocks.
> +	 */
> +int usb_max_xfer_blk = 4096;
> +#else
> +int usb_max_xfer_blk = 20;
> +#endif

This all looks horribly wrong and exactly what
7d6fd7f0ba71cd93d94079132f958d9630f27a89 and
02b0e1a36c5bc20174299312556ec4e266872bd6 fixed properly.

All those "dynamic reduction of transfer size" attempts are nonsensical,
the real solution (sadly) is to reduce the transfer size to cater for
the most limited devices and profile/fix the remaining delays in the USB
stack (which should have already been done, see the commits above). This
is also what the Linux USB stack does.

What is the problem you are trying to solve here ?