| Message ID | 20170219182918.4978-2-fschaefer.oss@googlemail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Em Sun, 19 Feb 2017 19:29:18 +0100 Frank Schäfer <fschaefer.oss@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.oss@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); Regards, Thanks, Mauro
Am 22.03.2017 um 15:46 schrieb Mauro Carvalho Chehab: > Em Sun, 19 Feb 2017 19:29:18 +0100 > Frank Schäfer <fschaefer.oss@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.oss@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 Regards, Frank > > Regards, > > Thanks, > Mauro
Em Thu, 23 Mar 2017 13:01:32 +0100 Frank Schäfer <fschaefer.oss@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.oss@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.oss@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
Am 23.03.2017 um 13:56 schrieb Mauro Carvalho Chehab: > Em Thu, 23 Mar 2017 13:01:32 +0100 > Frank Schäfer <fschaefer.oss@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.oss@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.oss@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. No, it should always be swapped, because the bytes are always transfered in the wrong order. The cpu endianess doesn't matter, (0x12 << 8) | 0x34 is always 0x1234. Regards, Frank > le16_to_cpu() should do the right thing, e. g. swap for BE > CPUs or not swap otherwise. > > Thanks, > Mauro
Em Thu, 23 Mar 2017 19:03:20 +0100 Frank Schäfer <fschaefer.oss@googlemail.com> escreveu: > Am 23.03.2017 um 13:56 schrieb Mauro Carvalho Chehab: > > Em Thu, 23 Mar 2017 13:01:32 +0100 > > Frank Schäfer <fschaefer.oss@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.oss@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.oss@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. > No, it should always be swapped, because the bytes are always transfered > in the wrong order. > The cpu endianess doesn't matter, (0x12 << 8) | 0x34 is always 0x1234. You still didn't get it. Let's assume that the ID is 0x148c (MT9M112). This value, represented in low endian, is stored in memory as: unsigned char __id[2] = { 0x8c, 0x14 }; If we do: u16 ret = *(u16 *)__id; What's stored at "ret" will depend if the sistem is LE or BE: on LE, ret == 0x148c on BE, ret == 0x8c14 If you do: u16 id = swapb16(val) you'll get: on LE, id == 0x8c14 on BE, id == 0x148c So, the value will be *wrong* at LE. However, if you do: id = le16_to_cpu((__le16)ret); On LE, this will evaluate to id = ret, and on BE, to id = swab16(ret). So, on both, you'll have: id = 0x148c. Thanks, Mauro
Am 24.03.2017 um 20:16 schrieb Mauro Carvalho Chehab: > Em Thu, 23 Mar 2017 19:03:20 +0100 > Frank Schäfer <fschaefer.oss@googlemail.com> escreveu: > >> Am 23.03.2017 um 13:56 schrieb Mauro Carvalho Chehab: >>> Em Thu, 23 Mar 2017 13:01:32 +0100 >>> Frank Schäfer <fschaefer.oss@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.oss@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.oss@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. >> No, it should always be swapped, because the bytes are always transfered >> in the wrong order. >> The cpu endianess doesn't matter, (0x12 << 8) | 0x34 is always 0x1234. > You still didn't get it. > > Let's assume that the ID is 0x148c (MT9M112). > > This value, represented in low endian, is stored in memory as: > > unsigned char __id[2] = { 0x8c, 0x14 }; > > If we do: > u16 ret = *(u16 *)__id; > > What's stored at "ret" will depend if the sistem is LE or BE: > > on LE, ret == 0x148c > on BE, ret == 0x8c14 > > If you do: > u16 id = swapb16(val) > > you'll get: > > on LE, id == 0x8c14 > on BE, id == 0x148c > > So, the value will be *wrong* at LE. > > However, if you do: > id = le16_to_cpu((__le16)ret); > > On LE, this will evaluate to id = ret, and on BE, to id = swab16(ret). > So, on both, you'll have: > id = 0x148c. Can you please show me the code line(s) that make the value of the word returned by i2c_smbus_read_word_data() cpu endianess dependent ? :) Cheers, Frank > > > Thanks, > Mauro
Am 26.03.2017 um 16:24 schrieb Frank Schäfer: > > > Am 24.03.2017 um 20:16 schrieb Mauro Carvalho Chehab: >> Em Thu, 23 Mar 2017 19:03:20 +0100 >> Frank Schäfer <fschaefer.oss@googlemail.com> escreveu: >> >>> Am 23.03.2017 um 13:56 schrieb Mauro Carvalho Chehab: >>>> Em Thu, 23 Mar 2017 13:01:32 +0100 >>>> Frank Schäfer <fschaefer.oss@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.oss@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.oss@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. >>> No, it should always be swapped, because the bytes are always >>> transfered >>> in the wrong order. >>> The cpu endianess doesn't matter, (0x12 << 8) | 0x34 is always 0x1234. >> You still didn't get it. >> >> Let's assume that the ID is 0x148c (MT9M112). >> >> This value, represented in low endian, is stored in memory as: >> >> unsigned char __id[2] = { 0x8c, 0x14 }; >> >> If we do: >> u16 ret = *(u16 *)__id; >> >> What's stored at "ret" will depend if the sistem is LE or BE: >> >> on LE, ret == 0x148c >> on BE, ret == 0x8c14 >> >> If you do: >> u16 id = swapb16(val) >> >> you'll get: >> >> on LE, id == 0x8c14 >> on BE, id == 0x148c >> >> So, the value will be *wrong* at LE. >> >> However, if you do: >> id = le16_to_cpu((__le16)ret); >> >> On LE, this will evaluate to id = ret, and on BE, to id = swab16(ret). >> So, on both, you'll have: >> id = 0x148c. > > Can you please show me the code line(s) that make the value of the > word returned by i2c_smbus_read_word_data() cpu endianess dependent ? :) > Ping !? Cheers, Frank
Em Mon, 10 Apr 2017 20:06:03 +0200 Frank Schäfer <fschaefer.oss@googlemail.com> escreveu: > Am 26.03.2017 um 16:24 schrieb Frank Schäfer: > > > > > > Am 24.03.2017 um 20:16 schrieb Mauro Carvalho Chehab: > >> Em Thu, 23 Mar 2017 19:03:20 +0100 > >> Frank Schäfer <fschaefer.oss@googlemail.com> escreveu: > >> > >>> Am 23.03.2017 um 13:56 schrieb Mauro Carvalho Chehab: > >>>> Em Thu, 23 Mar 2017 13:01:32 +0100 > >>>> Frank Schäfer <fschaefer.oss@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.oss@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.oss@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. > >>> No, it should always be swapped, because the bytes are always > >>> transfered > >>> in the wrong order. > >>> The cpu endianess doesn't matter, (0x12 << 8) | 0x34 is always 0x1234. > >> You still didn't get it. > >> > >> Let's assume that the ID is 0x148c (MT9M112). > >> > >> This value, represented in low endian, is stored in memory as: > >> > >> unsigned char __id[2] = { 0x8c, 0x14 }; > >> > >> If we do: > >> u16 ret = *(u16 *)__id; > >> > >> What's stored at "ret" will depend if the sistem is LE or BE: > >> > >> on LE, ret == 0x148c > >> on BE, ret == 0x8c14 > >> > >> If you do: > >> u16 id = swapb16(val) > >> > >> you'll get: > >> > >> on LE, id == 0x8c14 > >> on BE, id == 0x148c > >> > >> So, the value will be *wrong* at LE. > >> > >> However, if you do: > >> id = le16_to_cpu((__le16)ret); > >> > >> On LE, this will evaluate to id = ret, and on BE, to id = swab16(ret). > >> So, on both, you'll have: > >> id = 0x148c. > > > > Can you please show me the code line(s) that make the value of the > > word returned by i2c_smbus_read_word_data() cpu endianess dependent ? :) > > > Ping !? Just found time today to read the code implementation for i2c_smbus_read_word_data(). i2c_smbus_read_word_data() indeed does: case I2C_SMBUS_WORD_DATA: case I2C_SMBUS_PROC_CALL: data->word = msgbuf1[0] | (msgbuf1[1] << 8); So, it indeed stores data correctly, no matter the CPU endiannes. So, the patch itself looks correct, but I found the description misleading. I would describe it as: Use i2c_smbus_read_word_data() instead of i2c_master_send() and i2c_master_recv() for reading the ID of Micorn sensors. i2c_smbus_read_word_data() assumes that byes are in little-endian, so, it uses: data->word = msgbuf1[0] | (msgbuf1[1] << 8); However, Micron datasheet describes the ID as if they were read in big-endian. So, we need to change the byte order in order to match the ID number as described on their datasheets. With changing the description to something like that: Acked-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Thanks, Mauro
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 */ /* Read chip ID from register 0xff */ - reg = 0xff; - ret = i2c_master_send(client, ®, 1); - if (ret < 0) { - dev_err(&dev->intf->dev, - "couldn't read from i2c device 0x%02x: error %i\n", - client->addr << 1, ret); - continue; - } - ret = i2c_master_recv(client, (u8 *)&id_be, 2); + ret = i2c_smbus_read_word_data(client, 0xff); if (ret < 0) { dev_err(&dev->intf->dev, "couldn't read from i2c device 0x%02x: error %i\n", @@ -151,10 +132,9 @@ static int em28xx_probe_sensor_micron(struct em28xx *dev) continue; } /* Validate chip ID to be sure we have a Micron device */ - if (id != be16_to_cpu(id_be)) + if (id != swab16(ret)) continue; /* Check chip ID */ - id = be16_to_cpu(id_be); switch (id) { case 0x1222: name = "MT9V012"; /* MI370 */ /* 640x480 */
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.oss@googlemail.com> --- drivers/media/usb/em28xx/em28xx-camera.c | 28 ++++------------------------ 1 file changed, 4 insertions(+), 24 deletions(-)