Messages in this thread | | | Subject | Re: [PATCH] i2c: Raise SDA for each received bit, if necessary | From | Thomas Zimmermann <> | Date | Thu, 12 May 2016 18:19:12 +0200 |
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Hi
Am 12.05.2016 um 11:05 schrieb Wolfram Sang: > Hi Thomas, > > On Wed, Apr 27, 2016 at 08:11:54PM +0200, Thomas Zimmermann wrote: >> Some I2C adapters don't raise SDA by themselves when sending a bit. This >> behavior can be seen with the DDC channel of SiS 300 graphics cards. > > I think you mean 'clients' or 'devices' here, not adapters (masters), > right?
Yes, sorry.
> So, it seems you have a bus without a pull-up resistor (or a > broken one?) but use now a push-pull design. This is against the I2C > standard and for most circiuts quite dangerous as it can lead to > shortcuts.
I see.
> Do you have any hints that the bus is designed this way? In which driver > do you want to use the new flag?
I was playing with the DRM framework and an old SiS graphics card. I discovered this issue while trying to read the EDID from the monitor.
I have a few other SiS cards/models here and they all expose this behavior. So I guess it's intentional(==cheaper?), although the HW docs don't seem mention it explicitly.
Best regards Thomas
> > Thanks, > > Wolfram >
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