I understand the concern. I'm aware code is sometimes marked as runtime compatible though it is actually not and meeting all the criteria to work in the runtime environment is non-trivial as you noted.
In response to series #2 patch #8, Andrew noted that the UEFI spec defines restrictions on Runtime Services callers that prohibit re-entry into the GetVariable () and GetNextVariableName () services. With this restriction in mind, I believe the polling can be removed and the lock simply serve as an indicator to SMM whether a SMI that invokes SetVariable () interrupted a runtime read. Thanks, Michael > -----Original Message----- > From: Laszlo Ersek <ler...@redhat.com> > Sent: Thursday, October 3, 2019 4:01 AM > To: Wu, Hao A <hao.a...@intel.com>; Kubacki, Michael A > <michael.a.kuba...@intel.com>; devel@edk2.groups.io > Cc: Bi, Dandan <dandan...@intel.com>; Ard Biesheuvel > <ard.biesheu...@linaro.org>; Dong, Eric <eric.d...@intel.com>; Gao, Liming > <liming....@intel.com>; Kinney, Michael D <michael.d.kin...@intel.com>; > Ni, Ray <ray...@intel.com>; Wang, Jian J <jian.j.w...@intel.com>; Yao, > Jiewen <jiewen....@intel.com> > Subject: Re: [PATCH V2 7/9] MdeModulePkg/Variable: Add RT GetVariable() > cache support > > On 10/03/19 10:04, Wu, Hao A wrote: > > Before any comment on the patch, since I am not experienced in the > > Variable driver, I would like to ask for help from other reviewers to > > look into this patch and provide feedbacks as well. Thanks in advance. > > > > With the above fact, some comments provided below maybe wrong. So > > please help to kindly correct me. > > > > > > Some general comments: > > 1. I am not sure if bringing the TimerLib dependency (delay in acquiring the > > runtime cache read lock) to variable driver (a software driver for the > > most > > part) is a good idea. > > I agree. Most TimerLib instances do not expect sharing the hardware with > the OS. > > > Another complication is if the hardware is accessed via MMIO (that is, not IO > ports). MMIO accesses are subject to page tables. > > Assuming that MicroSecondDelay() is invoked from the runtime DXE driver at > OS runtime, a platform would have to expose the MMIO area of the timer > hardware in the UEFI memory map as "runtime MMIO". (Via GCD memory > space operations in a platform driver or in the TimerLib constructor.) > > Furthermore, the constructor function of the TimerLib instance would have > to register a VirtualAddressChange event handler, and convert the MMIO > address. > > Thanks > Laszlo -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#48452): https://edk2.groups.io/g/devel/message/48452 Mute This Topic: https://groups.io/mt/34318592/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
