[PATCH] docs: add more information about CXL2.0 device type

[luzhixing12345]

Add more information with CXL type1 and type2 devices.

Original doc says "May also have device private memory accessible 
via means such as PCI memory reads and writes to BARs.", but actually
CXL type1 devices doesn't have device memory.

Signed-off-by: luzhixing12345 <luzhixing12345@gmail.com>
---
 docs/system/devices/cxl.rst | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/docs/system/devices/cxl.rst b/docs/system/devices/cxl.rst
index 882b036f5e..ee50a3c18d 100644
--- a/docs/system/devices/cxl.rst
+++ b/docs/system/devices/cxl.rst
@@ -46,20 +46,14 @@ CXL 2.0 Device Types
 --------------------
 CXL 2.0 End Points are often categorized into three types.
 
-**Type 1:** These support coherent caching of host memory.  Example might
-be a crypto accelerators.  May also have device private memory accessible
-via means such as PCI memory reads and writes to BARs.
+**Type 1: Accelerators without device memory**. These support coherent caching 
of host memory. Example might be a crypto accelerators or smart NICs that use 
coherency semantics along with PCIe-style DMA transfers. Type1 devices 
implement a fully coherent cache but no host-managed device memory.
 
-**Type 2:** These support coherent caching of host memory and host
-managed device memory (HDM) for which the coherency protocol is managed
-by the host. This is a complex topic, so for more information on CXL
-coherency see the CXL 2.0 specification.
+**Type 2: Accelerators with device memory**. These support coherent caching of 
host memory and host managed device memory (HDM) for which the coherency 
protocol is managed by the host. Type 2 devices are accelerators such as 
GP-GPUs and FPGAs with device memory that can be mapped in part to the 
cacheable system memory. These devices also cache system memory for processing.
 
-**Type 3 Memory devices:**  These devices act as a means of attaching
-additional memory (HDM) to a CXL host including both volatile and
-persistent memory. The CXL topology may support interleaving across a
-number of Type 3 memory devices using HDM Decoders in the host, host
-bridge, switch upstream port and endpoints.
+**Type 3: Memory devices**. These devices act as a means of attaching
+additional memory (HDM) to a CXL host with different memory types, including 
supporting multiple memory tiers attached to the device with both volatile and 
persistent memory. The CXL topology may support interleaving across a number of 
Type 3 memory devices using HDM Decoders in the host, host bridge, switch 
upstream port and endpoints.
+
+See more information about CXL.io CXL.cache CXL.mem in the `CXL 2.0 
specification 
<https://computeexpresslink.org/past-cxl-specifications-landing-page/>`_.
 
 Scope of CXL emulation in QEMU
 ------------------------------
-- 
2.34.1