summaryrefslogtreecommitdiffstats
path: root/drivers/bcma/README
diff options
context:
space:
mode:
Diffstat (limited to 'drivers/bcma/README')
-rw-r--r--drivers/bcma/README19
1 files changed, 19 insertions, 0 deletions
diff --git a/drivers/bcma/README b/drivers/bcma/README
new file mode 100644
index 0000000..f7e7ce4
--- /dev/null
+++ b/drivers/bcma/README
@@ -0,0 +1,19 @@
+Broadcom introduced new bus as replacement for older SSB. It is based on AMBA,
+however from programming point of view there is nothing AMBA specific we use.
+
+Standard AMBA drivers are platform specific, have hardcoded addresses and use
+AMBA standard fields like CID and PID.
+
+In case of Broadcom's cards every device consists of:
+1) Broadcom specific AMBA device. It is put on AMBA bus, but can not be treated
+ as standard AMBA device. Reading it's CID or PID can cause machine lockup.
+2) AMBA standard devices called ports or wrappers. They have CIDs (AMBA_CID)
+ and PIDs (0x103BB369), but we do not use that info for anything. One of that
+ devices is used for managing Broadcom specific core.
+
+Addresses of AMBA devices are not hardcoded in driver and have to be read from
+EPROM.
+
+In this situation we decided to introduce separated bus. It can contain up to
+16 devices identified by Broadcom specific fields: manufacturer, id, revision
+and class.
OpenPOWER on IntegriCloud