Hello Frank,
Am Wed, 02 Jan 2013 22:25:10 +0100
schrieb Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx>:
> Hi Sascha,
>
> Am 02.01.2013 21:45, schrieb Sascha Sommer:
> > Hello,
> >
> > Am Sat, 22 Dec 2012 22:07:46 -0200
> > schrieb Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>:
> >
> >> Em Sun, 16 Dec 2012 19:23:28 +0100
> >> Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx> escreveu:
> >>
> >>> The em2800 can transfer up to 4 bytes per i2c message.
> >>> All other em25xx/em27xx/28xx chips can transfer at least 64 bytes
> >>> per message.
> >>>
> >>> I2C adapters should never split messages transferred via the I2C
> >>> subsystem into multiple message transfers, because the result will
> >>> almost always NOT be the same as when the whole data is
> >>> transferred to the I2C client in a single message.
> >>> If the message size exceeds the capabilities of the I2C adapter,
> >>> -EOPNOTSUPP should be returned.
> >>>
> >>> Signed-off-by: Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx>
> >>> ---
> >>> drivers/media/usb/em28xx/em28xx-i2c.c | 44
> >>> ++++++++++++++------------------- 1 Datei geändert, 18 Zeilen
> >>> hinzugefügt(+), 26 Zeilen entfernt(-)
> >>>
> >>> diff --git a/drivers/media/usb/em28xx/em28xx-i2c.c
> >>> b/drivers/media/usb/em28xx/em28xx-i2c.c index 44533e4..c508c12
> >>> 100644 --- a/drivers/media/usb/em28xx/em28xx-i2c.c
> >>> +++ b/drivers/media/usb/em28xx/em28xx-i2c.c
> >>> @@ -50,14 +50,18 @@ do
> >>> { \ } while
> >>> (0)
> >>> /*
> >>> - * em2800_i2c_send_max4()
> >>> - * send up to 4 bytes to the i2c device
> >>> + * em2800_i2c_send_bytes()
> >>> + * send up to 4 bytes to the em2800 i2c device
> >>> */
> >>> -static int em2800_i2c_send_max4(struct em28xx *dev, u8 addr, u8
> >>> *buf, u16 len) +static int em2800_i2c_send_bytes(struct em28xx
> >>> *dev, u8 addr, u8 *buf, u16 len) {
> >>> int ret;
> >>> int write_timeout;
> >>> u8 b2[6];
> >>> +
> >>> + if (len < 1 || len > 4)
> >>> + return -EOPNOTSUPP;
> >>> +
> >> Except if you actually tested it with all em2800 devices, I think
> >> that this change just broke it for em2800.
> >>
> >> Maybe Sascha could review this patch series on his em2800 devices.
> >>
> >> Those devices are limited, and just like other devices (cx231xx for
> >> example), the I2C bus need to split long messages, otherwise the
> >> I2C devices will fail.
> >>
> > The only device that I own is the Terratec Cinergy 200 USB.
> > Unfortunately I left it in my parents house so I won't be able to
> > test the patch within the next two weeks. I don't know if any of the
> > other devices ever transfered more than 4 bytes but as far as I
> > remember the windows driver of the cinergy 200 usb did not do this.
> > The traces obtained from it were the only information I had during
> > development. On first sight, the splitting code looks wrong.
>
> Thanks for your reply !
> I have a Terratec Cinergy 200 USB, too, and I used this device for
> testing the code.
> You are right, the Windows driver never transfers more than 4 bytes
> (verified with USB-logs).
> Do you know if there is something like a control flag for non-stopping
> i2c transfers ?
I never encountered such a flag.
>
> Maybe you also noticed the following tread:
> http://www.spinics.net/lists/linux-media/msg57442.html
>
> Do you remember any details about your device ?
The description in this thread also matches my device.
Maybe an additional hint is that it can't capture at full
resolution because the USB packet size is to small. Therefore
the em28xx driver somewhere limits it to 360x576 for PAL (Some commits
broke this code in the past)
> One thing not mentioned in this tread is, that there seem to be
> multiple chip IDs for the EM2800.
> The em28xx only knows about ID=7 and I assume that's what you device
> uses. But the chip in my device uses ID=4...
I checked some of my old mails. The original driver used the
chip id for device detection because some users had different devices
with different ids but this might have been a coincidence.
Judging from the patch below my card uses chip id 4, too.
---
25/drivers/media/video/em28xx/em28xx-cards.c~v4l-786-chip-id-removed-since-it-isn-t-required
Fri Nov 4 16:20:36 2005 +++
25-akpm/drivers/media/video/em28xx/em28xx-cards.c Fri Nov 4
16:20:37 2005 @@ -160,7 +160,6 @@ struct em2820_board em2820_boards[] =
{ }, [EM2800_BOARD_TERRATEC_CINERGY_200] = { .name = "Terratec
Cinergy 200 USB",
- .chip_id = 0x4,
.is_em2800 = 1,
.vchannels = 3,
.norm = VIDEO_MODE_PAL,
@@ -184,7 +183,6 @@ struct em2820_board em2820_boards[] = {
},
[EM2800_BOARD_LEADTEK_WINFAST_USBII] = {
.name = "Leadtek Winfast USB II",
- .chip_id = 0x2,
.is_em2800 = 1,
.vchannels = 3,
.norm = VIDEO_MODE_PAL,
@@ -208,7 +206,6 @@ struct em2820_board em2820_boards[] = {
},
[EM2800_BOARD_KWORLD_USB2800] = {
.name = "Kworld USB2800",
- .chip_id = 0x7,
.is_em2800 = 1,
.vchannels = 3,
.norm = VIDEO_MODE_PAL,
Regards
Sascha
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