Messages in this thread | | | Subject | Re: RFC: Using regmap in ARM64 for EL3 register access | From | Thor Thayer <> | Date | Wed, 4 Apr 2018 13:18:02 -0500 |
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Hi Sudeep,
On 04/04/2018 05:47 AM, Sudeep Holla wrote: > > > On 30/03/18 00:00, Thor Thayer wrote: >> Hi, >> >> I'm working on an ARM64 architecture that needs to manipulate some >> protected registers that are only accessible in EL3. Linux is running at >> EL1 which doesn't have the proper permissions for these registers. >> > If the hardware/IP registers are designed not to provide access to EL1, > then providing one in software by some means is simply wrong approach to > solve whatever issue you are trying to address here. > Thank you for the reply!
Sorry, I didn't describe this very well. This mechanism is similar to PSCI. We have System Management registers that could be needed by more than 1 virtual machine. So arbitration is needed and we use U-Boot for this.
>> Since U-Boot is running at the higher EL3, we communicate to the U-Boot >> functions through a SMC mechanism. >> > Please follow SMCCC to add any SMC interface. > Yes, the existing implementation is doing this and implements a SiP service framework.
>> The regmap framework seems like a good match for accessing these >> registers. We need the same functionality as I2C and SPI regmaps - read, >> write, and update registers. >> > No, providing register access to EL1 using regmap+SMC just defeats the > hardware security restrictions and may provide ways to exploit. > Why not abstract to the level of services you need ? > I'm not following about abstracting the level of services. For accessing the registers, I thought a regmap implementation would be nice because of the read/write/update functionality that would wrap around the SMC SiP service functions.
>> Any comments or suggestions about using regmap for this purpose? Is >> there a better method? >> > If you are looking for power management features, then PSCI and SCMI are > couple of specifications to look at. I would really like to know more > details on your use case to provide any suggestions. > Thank you for those pointers. I vaguely knew about PSCI but I wasn't aware of SCMI. Let me study these interfaces, particularly SCMI, before I reply further because this may answer many of my questions.
Thank you again,
Thor
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