Hi Guenter, On Tue, 2012-10-02 at 22:07 -0700, Guenter Roeck wrote: > On Tue, Oct 02, 2012 at 11:33:27PM -0400, Vivien Didelot wrote: > > From: Guillaume Roguez <[email protected]> > > > > The ADS7830 device is almost the same as the ADS7828, > > except that it does 8-bit sampling, instead of 12-bit. > > This patch extends the ads7828 driver to support this chip. > > > > Signed-off-by: Guillaume Roguez <[email protected]> > > Signed-off-by: Vivien Didelot <[email protected]> > > Guillaume, > Vivien, > > [ ... ] > > > @@ -147,6 +152,7 @@ static int ads7828_detect(struct i2c_client *client, > > { > > struct i2c_adapter *adapter = client->adapter; > > u8 default_cmd_byte = ADS7828_CMD_SD_SE | ADS7828_CMD_PD3; > > + bool is_8bit = false; > > int ch; > > > > /* Check we have a valid client */ > > @@ -158,7 +164,9 @@ static int ads7828_detect(struct i2c_client *client, > > * dedicated register so attempt to sanity check using knowledge of > > * the chip > > * - Read from the 8 channel addresses > > - * - Check the top 4 bits of each result are not set (12 data bits) > > + * - Check the top 4 bits of each result: > > + * - They should not be set in case of 12-bit samples > > + * - The two bytes should be equal in case of 8-bit samples > > */ > > for (ch = 0; ch < ADS7828_NCH; ch++) { > > u8 cmd = ads7828_cmd_byte(default_cmd_byte, ch); > > @@ -168,13 +176,20 @@ static int ads7828_detect(struct i2c_client *client, > > return -ENODEV; > > > > if (in_data & 0xF000) { > > - pr_debug("%s : Doesn't look like an ads7828 device\n", > > - __func__); > > - return -ENODEV; > > + if ((in_data >> 8) == (in_data & 0xFF)) { > > + /* Seems to be an ADS7830 (8-bit sample) */ > > + is_8bit = true; > > + } else { > > + dev_dbg(&client->dev, "doesn't look like an > > ADS7828 compatible device\n"); > > + return -ENODEV; > > + } > > } > > } > > I have been thinking about this. The detection function is already quite weak, > and this makes it even weaker. Reason is that you conly check for ADS7830 if > the > check for ADS7828 failed, and you repeat the pattern for each channel. > Unfortunately, that means that you don't check for the ADS7830 condition if > the > value returned for a channel happens to be a valid ADS7828 value, even if it > is > not valid for ADS7830 (and even if you already know that the chip is not a > ADS7828). > > Example: > ch=0: 0x1818 --> You know it is not ADS7828 > ch=1: 0x0818 --> You know it is not ADS7830, but you don't check for > it > > I don't know an optimal solution right now, but maybe something like > > maybe_7828 = true; > maybe_7830 = true; > for (ch = 0; ch < ADS7828_NCH && (maybe_7828 || maybe_7830); ch++) { > ... > if (in_data & 0xF000) > maybe_7828 = false; > if ((in_data >> 8) != (in_data & 0xFF)) > maybe_7830 = false; > } > if (!maybe_7828 && !maybe_7830) > return -ENODEV; > > if (maybe_7828) > strlcpy(info->type, "ads7828", I2C_NAME_SIZE); > else > strlcpy(info->type, "ads7830", I2C_NAME_SIZE); > > Frankly I would prefer to get rid of the _detect function entirely, I just > don't > know if that would negatively affect some users. To give you an example for a > bad result: The function will wrongly detect an ADS7830 as ADS7828 if all ADC > channels report a value between 0x00 and 0x0f.
We totally agree with you here. There is no clean way to detect (i.e. to be sure) that this *is* an ADS7828 compatible device. > How do you use the chip ? Do you need the detect function in your application > ? In our application, this device is statically declared in the platform support code, so we don't need to "detect" it. I propose to re-send a v5 with the "s/u16 in_data/int in_data/" fix and the ads7828_detect() removal in the first cleanup patch, then the ADS7830 support. Does it sound good for you? Thanks, Vivien -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
