Messages in this thread | | | Date | Thu, 11 Jan 2024 12:08:20 -0700 | Subject | Re: [PATCH] bus: mhi: host: Add sysfs entry to force device to enter EDL | From | Jeffrey Hugo <> |
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On 1/9/2024 2:20 AM, Qiang Yu wrote: > > On 1/3/2024 12:52 AM, Manivannan Sadhasivam wrote: >> On Tue, Jan 02, 2024 at 08:31:15AM -0700, Jeffrey Hugo wrote: >>> On 12/25/2023 12:47 AM, Qiang Yu wrote: >>>> From: Bhaumik Bhatt <quic_bbhatt@quicinc.com> >>>> >>>> Forcing the device (eg. SDX75) to enter Emergency Download Mode >>>> involves >>>> writing the 0xEDEDEDED cookie to the channel 91 doorbell register and >>>> forcing an SOC reset afterwards. Allow users of the MHI bus to >>>> exercise the >>>> sequence using a sysfs entry. >>> I don't see this documented in the spec anywhere. Is this standard >>> behavior >>> for all MHI devices? >>> >>> What about devices that don't support EDL mode? >>> >>> How should the host avoid using this special cookie when EDL mode is not >>> desired? >>> >> All points raised by Jeff are valid. I had discussions with Hemant and >> Bhaumik >> previously on allowing the devices to enter EDL mode in a generic >> manner and we >> didn't conclude on one final approach. >> >> Whatever way we come up with, it should be properly described in the >> MHI spec >> and _should_ be backwards compatible. > > Hi Mani, Jeff. The method of entering EDL mode is documented in MHI spec > v1.2, Chapter 13.2. > > Could you please check once?
I do see it listed there. However that was a FR for SDX55, so devices prior to that would not support this. AIC100 predates this change and would not support the functionality. I verified the AIC100 implementation is not aware of this cookie.
Also, that functionality depends on channel 91 being reserved per the table 9-2, however that table only applies to modem class devices as it is under chapter 9 "Modem protocols over PCIe". Looking at the ath11k and ath12k implementations in upstream, it looks like they partially comply. Other devices have different MHI channel definitions.
Chapter 9 doesn't appear to be in older versions of the spec that I have, so it is unclear if this functionality is backwards compatible (was channel 91 used for another purpose in pre-SDX55 modems).
I'm not convinced this belongs in the MHI core. At a minimum, the MHI controller(s) for the applicable devices needs to opt-in to this.
-Jeff
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