On 20.01.2025 3:41 PM, Johan Hovold wrote: > This series adds support for utilising the UEFI firmware RTC offset to > the Qualcomm PMIC RTC driver and uses that to enable the RTC on all X > Elite machines. > > Included is also a patch to switch the Lenovo ThinkPad X13s over to > using the UEFI offset. > > The RTCs in many Qualcomm devices are effectively broken due to the time > registers being read-only. Instead some other non-volatile memory can be > used to store an offset which a driver can take into account. On Windows > on Arm laptops, the UEFI firmware (and Windows) use a UEFI variable for > storing such an offset. > > When RTC support for the X13s was added two years ago we did not yet > have UEFI variable support for these machines in mainline and there were > also some concerns regarding flash wear. [1] As not all Qualcomm > platforms have UEFI firmware anyway, we instead opted to use a PMIC > scratch register for storing the offset. [2] > > On the UEFI machines in question this is however arguable not correct > as it means that the RTC time can differ between the UEFI firmware (and > Windows) and Linux. > > Now that the (reverse engineered) UEFI variable implementation has been > merged and thoroughly tested, let's switch to using that to store the > RTC offset also on Linux. The flash wear concerns can be mitigated by > deferring writes due to clock drift until shutdown. > > Note that this also avoids having to wait for months for Qualcomm to > provide a free PMIC SDAM scratch register for X1E and future platforms, > and specifically allows us to enable the RTC on X1E laptops today. > > Rob had some concerns about adding a DT property for indicating that a > machine uses UEFI for storing the offset and suggested that the driver > should probe for this instead. Unfortunately, this is easier said than > done given that UEFI variable support itself is probed for and may not > be available until after the RTC driver probes. > > Hopefully this all goes away (for future platforms) once Qualcomm fix > their UEFI implementation so that the UEFI time (and variable) services > can be used directly. > > Johan Thanks for working on this! Konrad
