Hi Daniel,
Thanks for the feedback.
On Tue, 3 Jul 2012 17:50:13 +0800, Daniel Kurtz wrote:
> On Tue, Jul 3, 2012 at 4:19 PM, Jean Delvare <khali@xxxxxxxxxxxx> wrote:
> >
> > Come up with a consistent, driver-wide strategy for event polling. For
> > intermediate steps of byte-by-byte block transactions, check for
> > BYTE_DONE or any error flag being set. At the end of every transaction,
> > check for both BUSY being cleared and INTR or any error flag being set.
> > This avoids having to wait twice for the same event.
> >
> > Signed-off-by: Jean Delvare <khali@xxxxxxxxxxxx>
> > Cc: Daniel Kurtz <djkurtz@xxxxxxxxxxxx>
> > ---
> > Daniel, this is what I had in mind. This applies on top of your first 6
> > patches (i.e. all the preliminary cleanup patches, not the interrupt
> > patches.) It solves the performance regression problem and makes the
> > code look better IMHO. Tested OK on ICH10 and ICH3-M. What do you
> > think? Comments and suggestions for improvements are very welcome.
> >
> > It may be possible to combine i801_wait_intr() and
> > i801_wait_byte_done() into a single function, as they do pretty much
> > the same, but I'll only do that if it doesn't hurt readability. My
> > first attempt was horrible.
> >
> > drivers/i2c/busses/i2c-i801.c | 88 ++++++++++++++++++++---------------------
> > 1 file changed, 43 insertions(+), 45 deletions(-)
> >
> > --- linux-3.5-rc5.orig/drivers/i2c/busses/i2c-i801.c 2012-07-02 18:09:59.000000000 +0200
> > +++ linux-3.5-rc5/drivers/i2c/busses/i2c-i801.c 2012-07-03 10:07:42.254632389 +0200
> > (...)
> > @@ -245,42 +245,60 @@ static int i801_check_post(struct i801_p
> > dev_dbg(&priv->pci_dev->dev, "Lost arbitration\n");
> > }
> >
> > - if (result) {
> > - /* Clear error flags */
> > - outb_p(status & STATUS_FLAGS, SMBHSTSTS(priv));
> > - status = inb_p(SMBHSTSTS(priv)) & STATUS_FLAGS;
> > - if (status) {
> > - dev_warn(&priv->pci_dev->dev, "Failed clearing status "
> > - "flags at end of transaction (%02x)\n",
> > - status);
> > - }
> > - }
> > + /* Clear status flags except BYTE_DONE, to be cleared by caller */
> > + clear = STATUS_ERROR_FLAGS;
> > + if (!(status & SMBHSTSTS_BYTE_DONE))
> > + clear |= SMBHSTSTS_INTR;
> > + outb_p(status & clear, SMBHSTSTS(priv));
>
> This becomes simpler (see below...), since status is already masked by
> (STATUS_ERROR_FLAGS | SMBHSTSTS_INTR).
>
> + outb_p(status, SMBHSTSTS(priv));
You're correct, I had not thought of doing it this way.
> >
> > return result;
> > }
> >
> > -/* wait for INTR bit as advised by Intel */
> > -static void i801_wait_intr(struct i801_priv *priv)
> > +/* Wait for BUSY being cleared and either INTR or an error flag being set */
> > +static int i801_wait_intr(struct i801_priv *priv)
> > {
> > int timeout = 0;
> > int status;
> >
> > + /* We will always wait for a fraction of a second! */
> > do {
> > usleep_range(250, 500);
> > status = inb_p(SMBHSTSTS(priv));
> > - } while ((!(status & SMBHSTSTS_INTR)) && (timeout++ < MAX_RETRIES));
> > + } while (((status & SMBHSTSTS_HOST_BUSY) ||
> > + !(status & (STATUS_ERROR_FLAGS | SMBHSTSTS_INTR))) &&
> > + (timeout++ < MAX_RETRIES));
>
>
> From your experiments, I think you saw that the final status (ERROR |
> INTR) will be set before or at the same time as HOST_BUSY -> 0, so the
> loop need only check HOST_BUSY, and then just return the final status
> bits of the transfer (ie, ERROR_FLAGS | INTR). So, the function name
> could be something like:
>
> i801_wait_xfer_status()
You're right. But I did these tests out of curiosity, maybe I shouldn't
have published the results, because now I feel reluctant to use the
results. The reason is that this is not specified in the datasheet, so
I have no guarantee that the same holds for all chips or all
transaction types.
Furthermore, I see no reason to not play it safe. What costs time and
CPU here is the sleep and the inb_p. The extra test is pretty cheap
IMHO.
> > (...)
> > +/* Wait for either BYTE_DONE or an error flag being set */
> > +static int i801_wait_byte_done(struct i801_priv *priv)
> > +{
> > + int timeout = 0;
> > + int status;
> > +
> > + /* We will always wait for a fraction of a second! */
> > + do {
> > + usleep_range(250, 500);
> > + status = inb_p(SMBHSTSTS(priv));
> > + } while (!(status & (STATUS_ERROR_FLAGS | SMBHSTSTS_BYTE_DONE)) &&
> > + (timeout++ < MAX_RETRIES));
> > +
> > + if (timeout > MAX_RETRIES) {
> > + dev_dbg(&priv->pci_dev->dev, "BYTE_DONE Timeout!\n");
> > + return -ETIMEDOUT;
> > + }
> > + return status;
> > }
>
> For i801_wait_byte_done(), on success I would return 0, if an error
> was set, return (status & ERROR_FLAG), and of course return -ETIMEDOUT
> on timeout.
> Then, we only need to call i801_check_post() if i801_wait_byte_done()
> != 0... see below...
Good idea, yes, this simplifies the code somewhat.
> >
> > static int i801_transaction(struct i801_priv *priv, int xact)
> > {
> > int status;
> > int result;
> > - int timeout = 0;
> >
> > result = i801_check_pre(priv);
> > if (result < 0)
> > @@ -290,19 +308,8 @@ static int i801_transaction(struct i801_
> > * SMBSCMD are passed in xact */
> > outb_p(xact | SMBHSTCNT_START, SMBHSTCNT(priv));
> >
> > - /* We will always wait for a fraction of a second! */
> > - do {
> > - usleep_range(250, 500);
> > - status = inb_p(SMBHSTSTS(priv));
> > - } while ((status & SMBHSTSTS_HOST_BUSY) && (timeout++ < MAX_RETRIES));
> > -
> > - result = i801_check_post(priv, status, timeout > MAX_RETRIES);
> > - if (result < 0)
> > - return result;
> > -
> > - i801_wait_intr(priv);
> > -
> > - return 0;
> > + status = i801_wait_intr(priv);
> > + return i801_check_post(priv, status);
> > }
> >
> > static int i801_block_transaction_by_block(struct i801_priv *priv,
> > @@ -353,7 +360,6 @@ static int i801_block_transaction_byte_b
> > int smbcmd;
> > int status;
> > int result;
> > - int timeout;
> >
> > result = i801_check_pre(priv);
> > if (result < 0)
> > @@ -381,15 +387,8 @@ static int i801_block_transaction_byte_b
> > outb_p(inb(SMBHSTCNT(priv)) | SMBHSTCNT_START,
> > SMBHSTCNT(priv));
> >
> > - /* We will always wait for a fraction of a second! */
> > - timeout = 0;
> > - do {
> > - usleep_range(250, 500);
> > - status = inb_p(SMBHSTSTS(priv));
> > - } while (!(status & (SMBHSTSTS_BYTE_DONE | STATUS_ERROR_FLAGS))
> > - && (timeout++ < MAX_RETRIES));
> > -
> > - result = i801_check_post(priv, status, timeout > MAX_RETRIES);
>
> + status = i801_wait_byte_done(priv);
> + if (status)
> + goto done;
That's not really different from my own code, I guess it depends if one
likes gotos or not.
> > @@ -421,9 +420,8 @@ static int i801_block_transaction_byte_b
> > outb_p(SMBHSTSTS_BYTE_DONE, SMBHSTSTS(priv));
> > }
> >
> > - i801_wait_intr(priv);
> > -
> > - return 0;
> > + status = i801_wait_intr(priv);
>
> done:
> > + return i801_check_post(priv, status);
> > }
> >
> > static int i801_set_block_buffer_mode(struct i801_priv *priv)
>
> While we are at this, let's clean up the "Illegal SMBus block read
> size" error path, as well.
> Why not use the "KILL" bit to terminate the transaction?
I have no idea why it was done that way, although I have to admit I'm
the author of the code (commit cf898dc5.) If using KILL works too and
this makes the core more simple, I'm all for it. This is easy enough to
test.
With your suggested changes, I have the following (tested) incremental
changes which I could merge into my patch. Please let me know if I
missed or misunderstood anything.
---
drivers/i2c/busses/i2c-i801.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
--- linux-3.5-rc5.orig/drivers/i2c/busses/i2c-i801.c 2012-07-03 15:00:21.000000000 +0200
+++ linux-3.5-rc5/drivers/i2c/busses/i2c-i801.c 2012-07-03 15:25:50.759652731 +0200
@@ -206,11 +206,14 @@ static int i801_check_pre(struct i801_pr
return 0;
}
-/* Convert the status register to an error code, and clear it. */
+/*
+ * Convert the status register to an error code, and clear it.
+ * Note that status only contains the bits we want to clear, not the
+ * actual register value.
+ */
static int i801_check_post(struct i801_priv *priv, int status)
{
int result = 0;
- int clear;
/* If the SMBus is still busy, we give up */
if (unlikely(status < 0)) {
@@ -246,10 +249,7 @@ static int i801_check_post(struct i801_p
}
/* Clear status flags except BYTE_DONE, to be cleared by caller */
- clear = STATUS_ERROR_FLAGS;
- if (!(status & SMBHSTSTS_BYTE_DONE))
- clear |= SMBHSTSTS_INTR;
- outb_p(status & clear, SMBHSTSTS(priv));
+ outb_p(status, SMBHSTSTS(priv));
return result;
}
@@ -272,7 +272,7 @@ static int i801_wait_intr(struct i801_pr
dev_dbg(&priv->pci_dev->dev, "INTR Timeout!\n");
return -ETIMEDOUT;
}
- return status;
+ return status & (STATUS_ERROR_FLAGS | SMBHSTSTS_INTR);
}
/* Wait for either BYTE_DONE or an error flag being set */
@@ -292,7 +292,7 @@ static int i801_wait_byte_done(struct i8
dev_dbg(&priv->pci_dev->dev, "BYTE_DONE Timeout!\n");
return -ETIMEDOUT;
}
- return status;
+ return status & STATUS_ERROR_FLAGS;
}
static int i801_transaction(struct i801_priv *priv, int xact)
@@ -388,9 +388,8 @@ static int i801_block_transaction_byte_b
SMBHSTCNT(priv));
status = i801_wait_byte_done(priv);
- result = i801_check_post(priv, status);
- if (result < 0)
- return result;
+ if (status)
+ goto exit;
if (i == 1 && read_write == I2C_SMBUS_READ
&& command != I2C_SMBUS_I2C_BLOCK_DATA) {
@@ -421,6 +420,7 @@ static int i801_block_transaction_byte_b
}
status = i801_wait_intr(priv);
+exit:
return i801_check_post(priv, status);
}
--
Jean Delvare
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