Re: [PATCH v4 01/11] drivers/char: Add support for USB3 DbC debugger

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.08.2022 03:38, Marek Marczykowski-Górecki wrote:
> From: Connor Davis <davisc@xxxxxxxxxxxx>
> 
> [Connor]
> Xue is a cross-platform USB 3 debugger that drives the Debug
> Capability (DbC) of xHCI-compliant host controllers. This patch
> implements the operations needed for xue to initialize the host
> controller's DbC and communicate with it. It also implements a struct
> uart_driver that uses xue as a backend. Note that only target -> host
> communication is supported for now. To use Xue as a console, add
> 'console=dbgp dbgp=xhci' to the command line.
> 
> [Marek]
> The Xue driver is taken from https://github.com/connojd/xue and heavily
> refactored to fit into Xen code base. Major changes include:
> - rename to xhci_dbc
> - drop support for non-Xen systems
> - drop xue_ops abstraction
> - use Xen's native helper functions for PCI access
> - move all the code to xue.c, drop "inline"
> - build for x86 only
> - annotate functions with cf_check
> - adjust for Xen's code style
> 
> At this stage, only the first xHCI is considered, and only output is
> supported. Later patches add support for choosing specific device, and
> input handling.
> The driver is initiallized before memory allocator works, so all the
> transfer buffers (about 230KiB of them) are allocated statically and will
> use memory even if XUE console is not selected. The driver can be
> disabled build time to reclaim this memory.
> Most of this memory is shared with the controller via DMA. Later patch
> will adjust structures placement to avoid anything else to be placed on
> those DMA-reachable pages. This also means str_buf cannot use static
> initializer, without reserving (at least) a whole page page in .data (or
> more, when combined with other structures).

While I still don't buy that the strings used here can't live next to
other string literals, ...

> Signed-off-by: Connor Davis <davisc@xxxxxxxxxxxx>
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan