RE: [RFC PATCH 1/4] usb: xhci: Synopsys xHC consolidate TRBs

[David Laight <David.Laight@ACULAB.COM>]

From: Tejas Joglekar
> Sent: 20 December 2019 13:39
>
> The Synopsys xHC has an internal TRB cache of size TRB_CACHE_SIZE for
> each endpoint. The default value for TRB_CACHE_SIZE is 16 for SS and 8
> for HS. The controller loads and updates the TRB cache from the transfer
> ring in system memory whenever the driver issues a start transfer or
> update transfer command.
> 
> For chained TRBs, the Synopsys xHC requires that the total amount of
> bytes for all TRBs loaded in the TRB cache be greater than or equal to 1
> MPS. Or the chain ends within the TRB cache (with a last TRB).
> 
> If this requirement is not met, the controller will not be able to send
> or receive a packet and it will hang causing a driver timeout and error.

This ought to be raised with Synopsys and they should be remake their
silicon to meet the XHCI standard and then offer to fix all the
boards that contain their broken version :-)

	David

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