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SubjectSPI <-> Parport (light) bridge code (Re: Stuck creating sysfs hooks for a driver..)
Jean Delvare wrote:

>Hi Kaiwan,

>You must stay away from writing a driver for the board itself. What you
>must write is in fact two different drivers:
>1* A driver for the SPI interface of your board (basically a parallel
>port <-> SPI bridge). This driver will expose the device as an SPI bus
>to the rest of the kernel. This driver doesn't care about what chip is
>plugged on it.
Hi Jean,

1. Yes, i know, long time since the above message..yet i'm happy to say
that i have built a (lightweight version) of the
SPI<->parport bridge (file pasted below), which is based on your
i2c-parport driver bridge code.
It is built as a header file: the driver developer basically appends
his/her adapter entry into the adapter_parm[] data structure and
includes this file in the device driver.

>2* A driver for the LM70 temperature sensor chip, which doesn't care
>about the chip location. This driver will use generic SPI commands as
>offered by the spi kernel interface.
>This modular approach makes it possible to then reuse each of the
>drivers. If you later have a similar board for a different chip, the
>first driver will still work (assuming the new board uses SPI and the
>same wiring conventions). If you later have an LM70 chip on a different
>physical interface, the second driver will still work.
2. I have also done this; i now have a working driver for a specific
chip (the NS lm70CILD-3 eval board) based on the (above mentioned)
SPi<->parport bridge. Basically, the "type 0" entry in the
adapter_parm[] data structure is the lm70CILD-3 entry. The driver
handles the other things, including creation of a sysfs hook (used to
query the temperature from userspace).

>No, just do what every other hardware monitoring chip does, so that
>support can be added for the lm70 chip in libsensors - then you win
>instant support in all hardware monitoring application which rely on
>libsensors, and even a few which do not.
>It's really not a matter of how many features a chip has. Look at the
>lm75 or w83l785ts driver, you'll see they have very few features as
>well. It's a matter of having a common standard for exporting the
>values to user-space, so that the same library or application can
>handle all sources with minimum effort.
3. I still have to work on integrating the userspace conversion into
libsensors (as recommended by yourself & others).

4. My intention at this point of time is for you (and others) to take a
look at the spi-parport-light.h code and pl give me your feedback. I'm
not posting a patch at this time..

5. Also, because it's a header, am not sure what approach to take when
patching into the kernel; i mean, i can place it under the spi tree
(either drivers/spi or include/linux/spi) but can't add the usual
"obj-$(CONFIG_xxx) += xxx.o"
line (as it's a header). Or can I do something like this?? i'm really
quite uncertain, forgive me.. any suggestions on how i should go about this?

Thanks very much,

PS> If you'd like to see a usage example, i can post the lm70CILD3.c
driver code..

+++++++++++++++++++++ File spi-parport-light.h
------------------------------------------------------------------------ *
spi-parport-light.h *
* SPI bus over parallel
port *
------------------------------------------------------------------------ *
Copyright (C) 2006 Kaiwan N Billimoria <>
Heavily based on i2c-parport-light.c
Copyright (C) 2003-2004 Jean Delvare <>

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
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., 675 Mass Ave, Cambridge, MA 02139, USA.
------------------------------------------------------------------------ */
#ifdef DATA
#undef DATA

#define DATA 0
#define STAT 1
#define CTRL 2

struct lineop {
u8 val;
u8 port;
u8 inverted;
struct adapter_parm {
char *name;
struct lineop setsda;
struct lineop setscl;
struct lineop setcsl; // chip select
struct lineop getsda;
struct lineop getscl;
struct lineop init;
struct spi_device *spidev;
static struct adapter_parm adapter_parm[] = {
/* type 0: National Semiconductor LM70CILD-3 evaluation board */
.name = "lm70CILD-3",
.setscl = { 0x40, DATA, 0 },
.setcsl = { 0x20, DATA, 1 },
.getsda = { 0x10, STAT, 0 }, // SI/O
.init = { 0xFE, DATA, 0 },
/* add adapters here */
/*----------------Module parameters-----------------------------*/
static int type;
module_param(type, int, 0);
"Type of adapter: (defaults to 0)\n"
" 0 = LM70CILD-3 (National Semiconductor) evaluation board\n");
/* add new type(s) here */
static u16 base;
module_param(base, ushort, 0);
MODULE_PARM_DESC(base, "Parport Base I/O address");
#include <linux/ioport.h>
#include <linux/delay.h>
#include <asm/io.h>

/* ----- Low-level parallel port access
----------------------------------- */
#define DEFAULT_BASE 0x378

static inline void port_write(unsigned char p, unsigned char d)
outb(d, base+p);
static inline unsigned char port_read(unsigned char p)
return inb(base+p);
/* ----- Unified line operation functions
--------------------------------- */
static inline void line_set(int state, const struct lineop *op)
u8 oldval = port_read(op->port);
/* Touch only the bit(s) needed */
if ((op->inverted && !state) || (!op->inverted && state))
port_write(op->port, oldval | op->val);
port_write(op->port, oldval & ~op->val);
static inline int line_get(const struct lineop *op)
u8 oldval = port_read(op->port);
return ((op->inverted && (oldval & op->val) != op->val)
|| (!op->inverted && (oldval & op->val) == op->val));
/* ----- SPI call-back functions and structures ----------------- */
static void parport_setscl(void *data, int state)
line_set(state, &adapter_parm[type].setscl);
static void parport_setsda(void *data, int state)
line_set(state, &adapter_parm[type].setsda);
static int parport_getscl(void *data)
return line_get(&adapter_parm[type].getscl);
static int parport_getsda(void *data)
return line_get(&adapter_parm[type].getsda);
static void parport_setcsl(void *data, int state)
line_set(state, &adapter_parm[type].setcsl);
/* ----- Module init and
exit---------------------------------------------- */
/* Module init : to be called from the specific driver init routine */
static int spi_parport_init(char *name)
/* adapter_parm set in the spi-parport-light.h header; type is a
module parameter */
if (type < 0 || type >= ARRAY_SIZE(adapter_parm)) {
printk(KERN_WARNING "%s: invalid parameter \"type\" (%d)\n\
defaulting to type 0\n", name, type);
type = 0;
if (base == 0)
if (!request_region(base, 3, "spi-parport-light"))
return -EBUSY;
/* Reset hardware to a sane state (SCL and SDA high) */
parport_setsda(NULL, 1);
parport_setscl(NULL, 1);
/* Other init if needed (power on...) */
if (adapter_parm[type].init.val)
line_set(1, &adapter_parm[type].init);
/* CS deselect, if necessary.. */
if (adapter_parm[type].setcsl.val)
line_set(0, &adapter_parm[type].setcsl);
/* Memory for the spi_device struct for this adapter */
adapter_parm[type].spidev = kzalloc(sizeof(struct spi_device),
if (!adapter_parm[type].spidev) {
printk(KERN_ERR "%s: out of memory\n", name);
release_region(base, 3);
return -ENOMEM;
printk(KERN_INFO "%s loaded: adapter type %d (device '%s'), using
base address 0x%x\n",
name, type, adapter_parm[type].name, base);

return 0;
/* Module exit : to be called from the specific driver cleanup routine */
static void spi_parport_exit(char *name)
if (adapter_parm[type].spidev)
kfree (adapter_parm[type].spidev);
/* Un-init if needed (power off...) */
if (adapter_parm[type].init.val)
line_set(0, &adapter_parm[type].init);
release_region(base, 3);
printk(KERN_INFO "%s unloaded.\n", name);
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