xref: /kernel/linux/linux-6.6/Documentation/driver-api/rapidio/tsi721.rst

=========================================================================
RapidIO subsystem mport driver for IDT Tsi721 PCI Express-to-SRIO bridge.
=========================================================================

1. Overview
===========

This driver implements all currently defined RapidIO mport callback functions.
It supports maintenance read and write operations, inbound and outbound RapidIO
doorbells, inbound maintenance port-writes and RapidIO messaging.

To generate SRIO maintenance transactions this driver uses one of Tsi721 DMA
channels. This mechanism provides access to larger range of hop counts and
destination IDs without need for changes in outbound window translation.

RapidIO messaging support uses dedicated messaging channels for each mailbox.
For inbound messages this driver uses destination ID matching to forward messages
into the corresponding message queue. Messaging callbacks are implemented to be
fully compatible with RIONET driver (Ethernet over RapidIO messaging services).

1. Module parameters:

- 'dbg_level'
      - This parameter allows to control amount of debug information
        generated by this device driver. This parameter is formed by set of
        This parameter can be changed bit masks that correspond to the specific
        functional block.
        For mask definitions see 'drivers/rapidio/devices/tsi721.h'
        This parameter can be changed dynamically.
        Use CONFIG_RAPIDIO_DEBUG=y to enable debug output at the top level.

- 'dma_desc_per_channel'
      - This parameter defines number of hardware buffer
        descriptors allocated for each registered Tsi721 DMA channel.
        Its default value is 128.

- 'dma_txqueue_sz'
      - DMA transactions queue size. Defines number of pending
        transaction requests that can be accepted by each DMA channel.
        Default value is 16.

- 'dma_sel'
      - DMA channel selection mask. Bitmask that defines which hardware
        DMA channels (0 ... 6) will be registered with DmaEngine core.
        If bit is set to 1, the corresponding DMA channel will be registered.
        DMA channels not selected by this mask will not be used by this device
        driver. Default value is 0x7f (use all channels).

- 'pcie_mrrs'
      - override value for PCIe Maximum Read Request Size (MRRS).
        This parameter gives an ability to override MRRS value set during PCIe
        configuration process. Tsi721 supports read request sizes up to 4096B.
        Value for this parameter must be set as defined by PCIe specification:
        0 = 128B, 1 = 256B, 2 = 512B, 3 = 1024B, 4 = 2048B and 5 = 4096B.
        Default value is '-1' (= keep platform setting).

- 'mbox_sel'
      - RIO messaging MBOX selection mask. This is a bitmask that defines
        messaging MBOXes are managed by this device driver. Mask bits 0 - 3
        correspond to MBOX0 - MBOX3. MBOX is under driver's control if the
        corresponding bit is set to '1'. Default value is 0x0f (= all).

2. Known problems
=================

  None.

3. DMA Engine Support
=====================

Tsi721 mport driver supports DMA data transfers between local system memory and
remote RapidIO devices. This functionality is implemented according to SLAVE
mode API defined by common Linux kernel DMA Engine framework.

Depending on system requirements RapidIO DMA operations can be included/excluded
by setting CONFIG_RAPIDIO_DMA_ENGINE option. Tsi721 miniport driver uses seven
out of eight available BDMA channels to support DMA data transfers.
One BDMA channel is reserved for generation of maintenance read/write requests.

If Tsi721 mport driver have been built with RAPIDIO_DMA_ENGINE support included,
this driver will accept DMA-specific module parameter:

  "dma_desc_per_channel"
			 - defines number of hardware buffer descriptors used by
                           each BDMA channel of Tsi721 (by default - 128).

4. Version History

  =====   ====================================================================
  1.1.0   DMA operations re-worked to support data scatter/gather lists larger
          than hardware buffer descriptors ring.
  1.0.0   Initial driver release.
  =====   ====================================================================

5.  License
===========

  Copyright(c) 2011 Integrated Device Technology, Inc. All rights reserved.

  This program is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the Free
  Software Foundation; either version 2 of the License, or (at your option)
  any later version.

  This program is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  more details.

  You should have received a copy of the GNU General Public License along with
  this program; if not, write to the Free Software Foundation, Inc.,
  59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.