Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 230 insertions, 0 deletions

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+================
+EISA bus support
+================
+
+:Author: Marc Zyngier <maz@wild-wind.fr.eu.org>
+
+This document groups random notes about porting EISA drivers to the
+new EISA/sysfs API.
+
+Starting from version 2.5.59, the EISA bus is almost given the same
+status as other much more mainstream busses such as PCI or USB. This
+has been possible through sysfs, which defines a nice enough set of
+abstractions to manage busses, devices and drivers.
+
+Although the new API is quite simple to use, converting existing
+drivers to the new infrastructure is not an easy task (mostly because
+detection code is generally also used to probe ISA cards). Moreover,
+most EISA drivers are among the oldest Linux drivers so, as you can
+imagine, some dust has settled here over the years.
+
+The EISA infrastructure is made up of three parts:
+
+    - The bus code implements most of the generic code. It is shared
+      among all the architectures that the EISA code runs on. It
+      implements bus probing (detecting EISA cards available on the bus),
+      allocates I/O resources, allows fancy naming through sysfs, and
+      offers interfaces for driver to register.
+
+    - The bus root driver implements the glue between the bus hardware
+      and the generic bus code. It is responsible for discovering the
+      device implementing the bus, and setting it up to be latter probed
+      by the bus code. This can go from something as simple as reserving
+      an I/O region on x86, to the rather more complex, like the hppa
+      EISA code. This is the part to implement in order to have EISA
+      running on an "new" platform.
+
+    - The driver offers the bus a list of devices that it manages, and
+      implements the necessary callbacks to probe and release devices
+      whenever told to.
+
+Every function/structure below lives in <linux/eisa.h>, which depends
+heavily on <linux/device.h>.
+
+Bus root driver
+===============
+
+::
+
+	int eisa_root_register (struct eisa_root_device *root);
+
+The eisa_root_register function is used to declare a device as the
+root of an EISA bus. The eisa_root_device structure holds a reference
+to this device, as well as some parameters for probing purposes::
+
+	struct eisa_root_device {
+		struct device   *dev;	 /* Pointer to bridge device */
+		struct resource *res;
+		unsigned long    bus_base_addr;
+		int		 slots;  /* Max slot number */
+		int		 force_probe; /* Probe even when no slot 0 */
+		u64		 dma_mask; /* from bridge device */
+		int              bus_nr; /* Set by eisa_root_register */
+		struct resource  eisa_root_res;	/* ditto */
+	};
+
+============= ======================================================
+node          used for eisa_root_register internal purpose
+dev           pointer to the root device
+res           root device I/O resource
+bus_base_addr slot 0 address on this bus
+slots	      max slot number to probe
+force_probe   Probe even when slot 0 is empty (no EISA mainboard)
+dma_mask      Default DMA mask. Usually the bridge device dma_mask.
+bus_nr	      unique bus id, set by eisa_root_register
+============= ======================================================
+
+Driver
+======
+
+::
+
+	int eisa_driver_register (struct eisa_driver *edrv);
+	void eisa_driver_unregister (struct eisa_driver *edrv);
+
+Clear enough ?
+
+::
+
+	struct eisa_device_id {
+		char sig[EISA_SIG_LEN];
+		unsigned long driver_data;
+	};
+
+	struct eisa_driver {
+		const struct eisa_device_id *id_table;
+		struct device_driver         driver;
+	};
+
+=============== ====================================================
+id_table	an array of NULL terminated EISA id strings,
+		followed by an empty string. Each string can
+		optionally be paired with a driver-dependent value
+		(driver_data).
+
+driver		a generic driver, such as described in
+		Documentation/driver-model/driver.txt. Only .name,
+		.probe and .remove members are mandatory.
+=============== ====================================================
+
+An example is the 3c59x driver::
+
+	static struct eisa_device_id vortex_eisa_ids[] = {
+		{ "TCM5920", EISA_3C592_OFFSET },
+		{ "TCM5970", EISA_3C597_OFFSET },
+		{ "" }
+	};
+
+	static struct eisa_driver vortex_eisa_driver = {
+		.id_table = vortex_eisa_ids,
+		.driver   = {
+			.name    = "3c59x",
+			.probe   = vortex_eisa_probe,
+			.remove  = vortex_eisa_remove
+		}
+	};
+
+Device
+======
+
+The sysfs framework calls .probe and .remove functions upon device
+discovery and removal (note that the .remove function is only called
+when driver is built as a module).
+
+Both functions are passed a pointer to a 'struct device', which is
+encapsulated in a 'struct eisa_device' described as follows::
+
+	struct eisa_device {
+		struct eisa_device_id id;
+		int                   slot;
+		int                   state;
+		unsigned long         base_addr;
+		struct resource       res[EISA_MAX_RESOURCES];
+		u64                   dma_mask;
+		struct device         dev; /* generic device */
+	};
+
+======== ============================================================
+id	 EISA id, as read from device. id.driver_data is set from the
+	 matching driver EISA id.
+slot	 slot number which the device was detected on
+state    set of flags indicating the state of the device. Current
+	 flags are EISA_CONFIG_ENABLED and EISA_CONFIG_FORCED.
+res	 set of four 256 bytes I/O regions allocated to this device
+dma_mask DMA mask set from the parent device.
+dev	 generic device (see Documentation/driver-model/device.txt)
+======== ============================================================
+
+You can get the 'struct eisa_device' from 'struct device' using the
+'to_eisa_device' macro.
+
+Misc stuff
+==========
+
+::
+
+	void eisa_set_drvdata (struct eisa_device *edev, void *data);
+
+Stores data into the device's driver_data area.
+
+::
+
+	void *eisa_get_drvdata (struct eisa_device *edev):
+
+Gets the pointer previously stored into the device's driver_data area.
+
+::
+
+	int eisa_get_region_index (void *addr);
+
+Returns the region number (0 <= x < EISA_MAX_RESOURCES) of a given
+address.
+
+Kernel parameters
+=================
+
+eisa_bus.enable_dev
+	A comma-separated list of slots to be enabled, even if the firmware
+	set the card as disabled. The driver must be able to properly
+	initialize the device in such conditions.
+
+eisa_bus.disable_dev
+	A comma-separated list of slots to be enabled, even if the firmware
+	set the card as enabled. The driver won't be called to handle this
+	device.
+
+virtual_root.force_probe
+	Force the probing code to probe EISA slots even when it cannot find an
+	EISA compliant mainboard (nothing appears on slot 0). Defaults to 0
+	(don't force), and set to 1 (force probing) when either
+	CONFIG_ALPHA_JENSEN or CONFIG_EISA_VLB_PRIMING are set.
+
+Random notes
+============
+
+Converting an EISA driver to the new API mostly involves *deleting*
+code (since probing is now in the core EISA code). Unfortunately, most
+drivers share their probing routine between ISA, and EISA. Special
+care must be taken when ripping out the EISA code, so other busses
+won't suffer from these surgical strikes...
+
+You *must not* expect any EISA device to be detected when returning
+from eisa_driver_register, since the chances are that the bus has not
+yet been probed. In fact, that's what happens most of the time (the
+bus root driver usually kicks in rather late in the boot process).
+Unfortunately, most drivers are doing the probing by themselves, and
+expect to have explored the whole machine when they exit their probe
+routine.
+
+For example, switching your favorite EISA SCSI card to the "hotplug"
+model is "the right thing"(tm).
+
+Thanks
+======
+
+I'd like to thank the following people for their help:
+
+- Xavier Benigni for lending me a wonderful Alpha Jensen,
+- James Bottomley, Jeff Garzik for getting this stuff into the kernel,
+- Andries Brouwer for contributing numerous EISA ids,
+- Catrin Jones for coping with far too many machines at home.