On Wed, 1 Feb 2023 at 17:09, Johan Hovold <johan@xxxxxxxxxx> wrote: > > [ +CC: Ard ] > > On Mon, Jan 30, 2023 at 12:49:44PM -0600, Rob Herring wrote: > > On Thu, Jan 26, 2023 at 03:20:51PM +0100, Johan Hovold wrote: > > > On many Qualcomm platforms the PMIC RTC control and time registers are > > > read-only so that the RTC time can not be updated. Instead an offset > > > needs be stored in some machine-specific non-volatile memory, which a > > > driver can take into account. > > > > > > Add a 'qcom,uefi-rtc-info' boolean flag which indicates that the RTC > > > offset is stored in a Qualcomm specific UEFI variable so that the RTC > > > time can be updated on such platforms. > > > > > > The UEFI variable is > > > > > > 882f8c2b-9646-435f-8de5-f208ff80c1bd-RTCInfo > > > > > > and holds a 12-byte structure where the first four bytes is a GPS time > > > offset in little-endian byte order. > > > > Can't you just try to read the UEFI variable and use it if that > > succeeds? > > Generally, yes. The problem here is that this UEFI variable is not used > on all devices using these PMICs and I need a way to determine whether > to wait for the UEFI variables to become available or not (e.g. when > efivars support is built as module, yes, that's a thing now...). > Could we read this variable at boot and pass it to the kernel in a different way? That way, we only have to defer the ability to set the RTC, right? > > I don't like this in DT because what if lots of devices start storing > > lots of things in vendor specific UEFI variables. It doesn't scale. > > I hope we won't see that even if we already have some devices for x86 > platforms storing MAC addresses and such in UEFI variables. They > currently access the UEFI firmware directly (i.e. not using the efivars > abstraction) and simply assume UEFI is always there. > > With the Google SMI efivars implementation or the new Qualcomm SMC-based > one, we need a way to determine whether to wait for efivars to become > registered. For drivers where efivars is always needed we can just probe > defer, but in this case we should not wait unless the DT indicates that > the RTC offset is stored in UEFI on this particular machine. > > Just as the nvmem-cell property indicates that the offset is stored in > some abstract nvmem, it seems reasonable to describe the offset being > stored in UEFI when that is the case (even if it is indeed generally > possible to probe for the latter). > > An alternative might be to describe the efivars fw dependency in DT too > (e.g. for device links), but I believe you have already expressed some > concerns over that: > > https://lore.kernel.org/lkml/20230130210530.GA3339716-robh@xxxxxxxxxx/ > > Johan
