Re: [RFC 0/2] sdhci-iproc CMD timeouts

On Thu, 25 Feb 2021 at 10:53, Nicolas Saenz Julienne
[off-list ref] wrote:

I'm seeing a rather odd behavior from sdhci-iproc's integration in BCM2711
(Raspberry Pi 4's SoC), and would appreciate some opinions.

The controller will timeout on SDHCI CMDs under the following conditions:

 - No SD card plugged in (the card polling thread is running, CD irq disabled).
 - BCM2711's VPU clock[1] configured at 500MHz or more, lower clocks are OK.

There is no specific command that will time out, it seems random.

Here's what I found out. The SDHCI controller runs at 100MHz, by bumping the
frequency to 150MHz the issue disapears. Might be pure luck, or maybe I hit the
nail and it's proper interference. Can't say.

As you probably know, I don't have the in-depth knowledge about this
HW. Although, let me provide a very vague guess. Could be that the
controller needs a higher clock rate to stay within some spec, for an
OPP/voltage domain for example?

In any case, assuming you get some confirmation from the Broadcom
folkz that this makes sense, you  need to update the DT doc bindings
to add the clock-frequency property. In regards to this, please take
the opportunity to convert from legacy DT doc format
(brcm,sdhci-iproc.txt) into the new yaml format.

Kind regards
Uffe

Regards,
Nicolas

---

[1] For those who are not aware, here's the relationship between VPU's clock
    and emmc2's:

         osc                                    54000000
            plld                              3000000091
               plld_per                        750000023
                  emmc2                        149882908
            pllc                              2999999988
               pllc_core0                      999999996
                  vpu                          499999998

Nicolas Saenz Julienne (2):
  ARM: dts: Fix-up EMMC2 controller's frequency
  mmc: sdhci-iproc: Set clock frequency as per DT

 arch/arm/boot/dts/bcm2711-rpi-4-b.dts |  6 ++++++
 drivers/mmc/host/sdhci-iproc.c        | 10 ++++++++++
 2 files changed, 16 insertions(+)

--
2.30.1

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