On Wed, Dec 31, 2025 at 09:51:13AM +0000, Luke Wang wrote: > > > > -----Original Message----- > > From: Marek Vasut <[email protected]> > > Sent: Tuesday, December 30, 2025 9:37 PM > > To: Luke Wang <[email protected]>; Peng Fan <[email protected]>; > > [email protected]; [email protected] > > Cc: [email protected]; [email protected]; > > [email protected]; [email protected]; [email protected]; > > [email protected]; Ye Li <[email protected]>; Bough Chen > > <[email protected]>; [email protected] > > Subject: [EXT] Re: [PATCH] mmc: Add power stabilization delay in > > mmc_power_on() > > > > Caution: This is an external email. Please take care when clicking links or > > opening attachments. When in doubt, report the message using the 'Report > > this > > email' button > > > > > > On 12/30/25 11:39 AM, [email protected] wrote: > > > From: Luke Wang <[email protected]> > > > > > > After enabling vmmc supply, add 10ms delay to allow voltage to > > > stabilize before SD initialization starts. Without this delay, > > > some SD cards fail to initialize because the initial clock cycles > > > are sent while power is still ramping up. > > Details please. Which exact cards ? With which controller/SoC ? Does > > this problem happen on another SoC/controller ? > > MMC initialization failed on IMX7ULP-EVK with the SanDisk Ultra > 64GB card (CID: 035344534436344785569a5ab5018400). However, > SanDisk Ultra 32GB and 16GB cards did not encounter this issue > (both have CID: 035344534331364780c86726e1012700). > > The root cause of this issue is that this SD card requires at > least 74 clock cycles after power-up, otherwise CMD8 will not > receive a response. For other SD cards that initialize normally, > the initial clock cycles are not mandatory - they can still > initialize successfully even without them. > > On the IMX7ULP-EVK, the SD power-up time takes approximately 2ms > to reach VDD MIN voltage. However, the current code does not wait > for the voltage to stabilize before sending the initial clock > cycles. This results in the VDD voltage being only around 1V when > the initial clock cycles are sent, causing the SD card to > completely miss these initial clock cycles. > > We could add regulator-ramp-delay or startup-delay-us values in > the dts vmmc regulator, but I have checked some dts files and > found that many of them do not configure these two values - not > just for the IMX series, but across different platforms. If we > were to add them in dts, it would require modifying a very large > number of dts files. > > Alternatively, we could follow the approach in the Linux kernel's > mmc_power_up() function and wait 10ms after power on. > > This card does not encounter issues on the IMX8MM platform because > the IMX8MM's SD power only needs about 0.5ms to stabilize. Sending > 1ms of initial clock cycles ensures that the SD card can still > receive at least 74 clock cycles after the voltage has stabilized. > Even though no issue was encountered, sending initial clocks during > the power ramp-up phase still does not comply with the description > in Section 6.4.1 of the SD Physical Layer Specification Version > 3.00. > > Additionally, I believe the 1000us delay at the beginning of the > mmc_go_idle() function exists for a similar reason. Without this > 1000us delay, CMD0 would be sent even before the voltage reaches > VDD_MIN. > > This should be a common issue, not limited to the IMX platform. > We can either add a delay in the code or add regulator-ramp-delay/ > startup-delay-us in numerous dts files.
Please condense this slightly and expand the commit message, thanks! -- Tom
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