linux-kernel - [RFC 0/2] sdhci-iproc CMD timeouts

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Message-Id: <20210225095216.28591-1-nsaenzjulienne@suse.de>
Date:   Thu, 25 Feb 2021 10:52:14 +0100
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     linux-arm-kernel@...ts.infradead.org, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org
Cc:     f.fainelli@...il.com, phil@...pberrypi.com,
        tim.gover@...pberrypi.com, adrian.hunter@...el.com,
        sbranden@...adcom.com, alcooperx@...il.com,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        linux-kernel@...r.kernel.org
Subject: [RFC 0/2] sdhci-iproc CMD timeouts

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.

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