Em Thu, 23 Mar 2017 13:01:32 +0100
Frank Schäfer <fschaefer....@googlemail.com> escreveu:
> Am 22.03.2017 um 15:46 schrieb Mauro Carvalho Chehab:
> > Em Sun, 19 Feb 2017 19:29:18 +0100
> > Frank Schäfer <fschaefer....@googlemail.com> escreveu:
> >
> >> Use i2c_smbus_read_word_data() instead of i2c_master_send() and
> >> i2c_master_recv() for reading the ID of Micorn sensors.
> >> Bytes need to be swapped afterwards, because i2c_smbus_read_word_data()
> >> assumes that the received bytes are little-endian byte order (as specified
> >> by smbus), while Micron sensors with 16 bit register width use big endian
> >> byte order.
> >>
> >> Signed-off-by: Frank Schäfer <fschaefer....@googlemail.com>
> >> ---
> >> drivers/media/usb/em28xx/em28xx-camera.c | 28
> >> ++++------------------------
> >> 1 file changed, 4 insertions(+), 24 deletions(-)
> >>
> >> diff --git a/drivers/media/usb/em28xx/em28xx-camera.c
> >> b/drivers/media/usb/em28xx/em28xx-camera.c
> >> index 7b4129ab1cf9..4839479624e7 100644
> >> --- a/drivers/media/usb/em28xx/em28xx-camera.c
> >> +++ b/drivers/media/usb/em28xx/em28xx-camera.c
> >> @@ -106,8 +106,6 @@ static int em28xx_probe_sensor_micron(struct em28xx
> >> *dev)
> >> {
> >> int ret, i;
> >> char *name;
> >> - u8 reg;
> >> - __be16 id_be;
> >> u16 id;
> >>
> >> struct i2c_client *client = &dev->i2c_client[dev->def_i2c_bus];
> >> @@ -115,10 +113,8 @@ static int em28xx_probe_sensor_micron(struct em28xx
> >> *dev)
> >> dev->em28xx_sensor = EM28XX_NOSENSOR;
> >> for (i = 0; micron_sensor_addrs[i] != I2C_CLIENT_END; i++) {
> >> client->addr = micron_sensor_addrs[i];
> >> - /* NOTE: i2c_smbus_read_word_data() doesn't work with BE data */
> >> /* Read chip ID from register 0x00 */
> >> - reg = 0x00;
> >> - ret = i2c_master_send(client, ®, 1);
> >> + ret = i2c_smbus_read_word_data(client, 0x00); /* assumes LE */
> >> if (ret < 0) {
> >> if (ret != -ENXIO)
> >> dev_err(&dev->intf->dev,
> >> @@ -126,24 +122,9 @@ static int em28xx_probe_sensor_micron(struct em28xx
> >> *dev)
> >> client->addr << 1, ret);
> >> continue;
> >> }
> >> - ret = i2c_master_recv(client, (u8 *)&id_be, 2);
> >> - if (ret < 0) {
> >> - dev_err(&dev->intf->dev,
> >> - "couldn't read from i2c device 0x%02x: error
> >> %i\n",
> >> - client->addr << 1, ret);
> >> - continue;
> >> - }
> >> - id = be16_to_cpu(id_be);
> >> + id = swab16(ret); /* LE -> BE */
> > That's wrong! You can't assume that CPU is BE, as some archs use LE.
> >
> > You should, instead, call le16_to_cpu(), to be sure that it will be
> > doing the right thing.
> >
> > Something like:
> >
> > id = le16_to_cpu((__le16)ret);
>
> SMBus read/write word transfers are always LE (see SMBus spec section
> 6.5.5),
> which is also what i2c_smbus_xfer_emulated() assumes:
> http://lxr.free-electrons.com/source/drivers/i2c/i2c-core.c#L3485
I got that part, but, if the CPU is also LE, doing swab16() is
wrong. It should swap it *only* if the CPU is BE.
le16_to_cpu() should do the right thing, e. g. swap for BE
CPUs or not swap otherwise.
Thanks,
Mauro
