linux/drivers/bcma/README

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.
bcma: add Broadcom specific AMBA bus driver Broadcom has released cards based on a new AMBA-based bus type. From a programming point of view, this new bus type differs from AMBA and does not use AMBA common registers. It also differs enough from SSB. We decided that a new bus driver is needed to keep the code clean. In its current form, the driver detects devices present on the bus and registers them in the system. It allows registering BCMA drivers for specified bus devices and provides them basic operations. The bus driver itself includes two important bus managing drivers: ChipCommon core driver and PCI(c) core driver. They are early used to allow correct initialization. Currently code is limited to supporting buses on PCI(e) devices, however the driver is designed to be used also on other hosts. The host abstraction layer is implemented and already used for PCI(e). Support for PCI(e) hosts is working and seems to be stable (access to 80211 core was tested successfully on a few devices). We can still optimize it by using some fixed windows, but this can be done later without affecting any external code. Windows are just ranges in MMIO used for accessing cores on the bus. Cc: Greg KH <greg@kroah.com> Cc: Michael Büsch <mb@bu3sch.de> Cc: Larry Finger <Larry.Finger@lwfinger.net> Cc: George Kashperko <george@znau.edu.ua> Cc: Arend van Spriel <arend@broadcom.com> Cc: linux-arm-kernel@lists.infradead.org Cc: Russell King <rmk@arm.linux.org.uk> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Andy Botting <andy@andybotting.com> Cc: linuxdriverproject <devel@linuxdriverproject.org> Cc: linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org> Signed-off-by: Rafał Miłecki <zajec5@gmail.com> Signed-off-by: John W. Linville <linville@tuxdriver.com> 2011-05-09 16:56:46 +00:00			`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.`