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X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR11MB7313 X-OriginatorOrg: intel.com On 4/23/2026 2:02 PM, David Airlie wrote: > On Fri, Apr 24, 2026 at 5:42 AM Jacob Keller wrote: >> >> On 4/23/2026 12:22 PM, Jocelyn Falempe wrote: >>> On 23/04/2026 18:35, Jacob Keller wrote: >>>> On 4/23/2026 12:44 AM, Thomas Zimmermann wrote: >>>>> Hi >>>>> >>>>> Am 23.04.26 um 01:55 schrieb Jacob Keller: >>>>>> Hello, >>>>>> >>> I'm also curious if its possible to stop polling for so >>> long with udelay >>>>>> in the i2c logic somehow? I am not very familiar with i2c, but it is >>>>>> frustrating that this driver is causing yet another stall that is >>>>>> impacting timing sensitive data. Even if in this case its due to a >>>>>> faulty cable.. it is frustrating that such result causes the PTP >>>>>> failures. Would switching to WQ_UNBOUND be helpful here at all? >>>>> >>>>> Try Dave's suggestion to avoid polling. The driver won't be able to >>>>> detect changes to the connector status, though. >>>>> >>>> >>>> That's fine. I don't think we're even using the device. It looks like it >>>> might only be in use for BMC, and the VGA connection isn't actually >>>> physically available, so there are no changes to detect. >>>> >>>> Is this polling really only to detect when VGA is enabled? Would it make >>>> sense to only poll on platforms which actually *have* that VGA >>> connection? >>>> >>> Polling was introduced with https://patchwork.freedesktop.org/ >>> series/131977/ >>> >>> The driver needs to know if a VGA monitor is connected or not, to >>> provide the right available resolutions to the userspace. >>> Otherwise you can set a high resolution that works from the BMC, but >>> then connecting a VGA monitor will not work, as the driver won't notice >>> that something has been connected. >>> >>> The mgag200 doesn't have an IRQ or a register to check if something is >>> connected on the VGA port, so the driver uses the i2c and tries to read >>> the EDID. >>> >>> Unfortunately, there is no way to know reliably if a VGA connector is >>> present. It's possible to disable polling on some machines using DMI >>> quirks, but I don't think this approach will scale. >>> >> >> Timing sensitive setups like mine must have system admins who know to >> manually disable mgag200 or disable polling. Many users won't be aware >> of this. If the polling were not intrusive, this would not be an issue. >> But.... >> >> Faulty hardware (perhaps just a cheap pull down resistor on the VGA >> connection as Dave Airlie suggests) means that any such affected >> platform has a polling routine that causes significant issues on any >> timing sensitive applications. > > We could write a patch to just say if we see 10 bogus EDID polls we > just give up and loudly say in the logs. > That would certainly be a better situation for me... > This might break some crash-cart plugins in some data centers though, > I don't think we have contracts in Matrox or the server vendors who > make the hw to say how they recommend finding this info. > But I could see this being a problem for data centers who previously saw "no issue" and now see "this device is causing a problem", especially if that problem is really non-existent? > It might be in ACPI or dmidecodes. > I can try checking if anything obvious shows up in dmidecodes for the device. > Dave.