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List: linux-i2c
Subject: Re: [PATCH/RFC] I2C host adapter slave support and ppc/mpc driver
From: Ben Dooks <ben-i2c () fluff ! org>
Date: 2010-08-31 22:30:17
Message-ID: 20100831223016.GB24761 () trinity ! fluff ! org
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On Mon, Jul 26, 2010 at 04:46:58PM +0200, Fillod Stephane wrote:
> Hi,
>
> For anyone interested, I have implemented i2c slave mode transfers.
>
> The i2c-dev subsystem is extended with a new flag I2C_M_SLAVE.
> Basically, a struct i2c_msg holding flag I2C_M_SLAVE will wait
> in slave mode for a write request on specified target address,
> and will report the received content to the user application.
>
> An example of driver implementation has been done for i2c-mpc.
> There's no support for read request yet, and I'm wondering whether
> it would make sense. The patch has been tested on powerpc MPC8313E.
> Note: the present i2c-mpc implementation may be improved,
> esp. regarding current timing issues.
>
> The need for I2C host adapter slave support is quite uncommon.
> Last question was raised 2 years ago[1].
> This kind of support can prove useful in multi-master based
> protocols like found in IPMI. With appropriate hacking,
> FreeIPMI[2] software can nicely make use of such subsystem.
>
> Talking about i2c-dev, does the I2C_M_SLAVE flag is the appropriate
> way of modelling the API extension? Is there any interest for
> this extension to be accepted in the linux kernel?
>
> Any comments, advices are welcome.
>
> [1] http://thread.gmane.org/gmane.linux.drivers.i2c/43/focus=43
> [2] http://www.gnu.org/software/freeipmi/
I'm sort of interested, as the samsung i2c core can also do slave
support, and the pxa used to have such an interface too.
My only concern is how to deal with the case where you have a fast
i2c bus and multiple transactions you need to process, such as a
write followed by a read, especially where transaction #1 affects
the contents of transaction #2
> Signed-off-by: Stephane Fillod <stephane.fillod@grassvalley.com>
>
> --- a/include/linux/i2c.h 24 Feb 2010 18:52:17 -0000
> +++ b/include/linux/i2c.h 26 Feb 2010 15:50:46 -0000
> @@ -492,6 +492,7 @@ struct i2c_msg {
> __u16 flags;
> #define I2C_M_TEN 0x0010 /* this is a ten bit chip
> address */
> #define I2C_M_RD 0x0001 /* read data, from slave to
> master */
> +#define I2C_M_SLAVE 0x0002 /* from master client to slave
> adap */
> #define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING
> */
> #define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING
> */
> #define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING
> */
> --- a/drivers/i2c/i2c-dev.c 24 Feb 2010 18:52:17 -0000
> +++ b/drivers/i2c/i2c-dev.c 26 Feb 2010 15:49:51 -0000
> @@ -270,12 +270,18 @@ static noinline int i2cdev_ioctl_rdrw(st
>
> res = i2c_transfer(client->adapter, rdwr_pa, rdwr_arg.nmsgs);
> while (i-- > 0) {
> - if (res >= 0 && (rdwr_pa[i].flags & I2C_M_RD)) {
> + if (res >= 0 && (rdwr_pa[i].flags &
> (I2C_M_RD|I2C_M_SLAVE))) {
> if (copy_to_user(data_ptrs[i], rdwr_pa[i].buf,
> rdwr_pa[i].len))
> res = -EFAULT;
> }
> kfree(rdwr_pa[i].buf);
> + if (res >= 0 && (rdwr_pa[i].flags & I2C_M_SLAVE)) {
> + struct i2c_msg __user *umsgs;
> + umsgs = ((struct i2c_rdwr_ioctl_data __user
> *)arg)->msgs;
> + if (put_user(rdwr_pa[i].len, &umsgs[i].len))
> + res = -EFAULT;
> + }
> }
> kfree(data_ptrs);
> kfree(rdwr_pa);
> --- a/drivers/i2c/busses/i2c-mpc.c 3 Dec 2009 03:51:21 -0000
> +++ b/drivers/i2c/busses/i2c-mpc.c 27 Apr 2010 11:01:47 -0000
> @@ -4,7 +4,7 @@
>
> * This is a combined i2c adapter and algorithm driver for the
> * MPC107/Tsi107 PowerPC northbridge and processors that include
> - * the same I2C unit (8240, 8245, 85xx).
> + * the same I2C unit (8240, 8245, 83xx, 85xx).
> *
> * Release 0.8
> *
> @@ -31,6 +31,7 @@
>
> #define DRV_NAME "mpc-i2c"
>
> +#define MPC_I2C_ADDR 0x00
> #define MPC_I2C_FDR 0x04
> #define MPC_I2C_CR 0x08
> #define MPC_I2C_SR 0x0c
> @@ -73,6 +74,11 @@ struct mpc_i2c_match_data {
> u32 prescaler;
> };
>
> +static inline void writeaddr(struct mpc_i2c *i2c, u32 x)
> +{
> + writeb(x, i2c->base + MPC_I2C_ADDR);
> +}
> +
> static inline void writeccr(struct mpc_i2c *i2c, u32 x)
> {
> writeb(x, i2c->base + MPC_I2C_CR);
> @@ -428,6 +434,68 @@ static int mpc_read(struct mpc_i2c *i2c,
> return length;
> }
>
> +static int mpc_slave_xrecv(struct mpc_i2c *i2c, int target,
> + u8 *data, int length, int restart)
> +{
> + unsigned timeout = i2c->adap.timeout;
> + int i, result, srw;
> + int readlen = 0;
> + u32 flags;
> +
> + /* Listening address */
> + writeaddr(i2c, target);
> + /* Start with MEN */
> + writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_MTX);
> +
> + /* Give I2C signals sufficent time to settle */
> + udelay(30);
> +
> + result = i2c_wait(i2c, timeout, 1);
> + if (result < 0) {
> + writeccr(i2c, 0);
> + return result;
> + }
> +#if 0
> + srw = readb(i2c->base + MPC_I2C_SR) & CSR_SRW;
> +#else
> + /* TODO: handle and test SRW!=0 */
> + srw = 0;
> +#endif
> + flags = srw ? CCR_MTX : 0;
> +
> + if (length) {
> + if (length == 1)
> + writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_TXAK |
> flags);
> + else
> + writeccr(i2c, CCR_MIEN | CCR_MEN | flags);
> + /* Dummy read/write */
> + if (srw)
> + writeb(0, i2c->base + MPC_I2C_DR);
> + else
> + readb(i2c->base + MPC_I2C_DR);
> + }
> +
> + for (i = 0; i < length; i++) {
> + result = i2c_wait(i2c, timeout, 0);
> + if (result < 0)
> + return i > 0 && result == -ETIMEDOUT ? i-1 :
> result;
> + /* Generate stop on last byte */
> + if (i == length - 1)
> + writeccr(i2c, CCR_MIEN | CCR_MEN | CCR_TXAK |
> flags);
> + data[i] = readb(i2c->base + MPC_I2C_DR);
> + readlen++;
> + /* check early STOP after 2 clock cycles at 100 kHz */
> + udelay(20);
> + if (!(readb(i2c->base + MPC_I2C_SR) & CSR_MBB))
> + break;
> + }
> + /* clear I2CSR register */
> + out_8(i2c->base + MPC_I2C_SR, 0);
> + /* hang up */
> + writeccr(i2c, CCR_MEN);
> + return readlen;
> +}
> +
> static int mpc_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int
> num)
> {
> struct i2c_msg *pmsg;
> @@ -459,9 +527,14 @@ static int mpc_xfer(struct i2c_adapter *
> pmsg = &msgs[i];
> dev_dbg(i2c->dev,
> "Doing %s %d bytes to 0x%02x - %d of %d
> messages\n",
> - pmsg->flags & I2C_M_RD ? "read" : "write",
> + pmsg->flags & I2C_M_SLAVE ? "recv" :
> + pmsg->flags & I2C_M_RD ? "read" :
> "write",
> pmsg->len, pmsg->addr, i + 1, num);
> - if (pmsg->flags & I2C_M_RD)
> + if (pmsg->flags & I2C_M_SLAVE) {
> + ret = mpc_slave_xrecv(i2c, pmsg->addr,
> pmsg->buf, pmsg->len, i);
> + if (ret >= 0)
> + pmsg->len = ret;
> + } else if (pmsg->flags & I2C_M_RD)
> ret =
> mpc_read(i2c, pmsg->addr, pmsg->buf,
> pmsg->len, i);
> else
>
>
> Regards
> --
> Stephane Fillod
> --
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--
--
Ben
Q: What's a light-year?
A: One-third less calories than a regular year.
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