linux-kernel - Re: SDHCI AM654 driver delaying boot time

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Date:   Thu, 9 Nov 2023 11:51:59 -0600
From:   Nishanth Menon <nm@...com>
To:     João Paulo Silva Gonçalves 
        <joao.goncalves@...adex.com>
CC:     "faiz_abbas@...com" <faiz_abbas@...com>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        Francesco Dolcini <francesco.dolcini@...adex.com>
Subject: Re: SDHCI AM654 driver delaying boot time

On 18:56-20231108, João Paulo Silva Gonçalves wrote:
> Hello all, 
> 
> We are trying to minimize boot time for our AM62 devices. Unfortunately, we have identified a delay of approximately 1.5 seconds caused by the
> sdhci_am654 driver. This delay is a result of a timeout within the driver (MAX_POWER_ON_TIMEOUT) and was introduced in commit 7ca0f16 ("mmc:
> sdhci_am654: Add workaround for card detect debounce timer"). This issue arises only when there is no SD card present in the MMC slot.  We tested the
> driver with a lower timeout value and everything worked. However, as indicated in the commit message, this timeout may be related to the way the sdhci
> controller hardware IP works. Currently, the driver employs a sort of a "busy loop" to wait for this timeout to pass delaying the boot. Why is
> need to busy loop for this timeout? Is it possible to wait for it in the backgroud? Am I am missing something here? 

I am not an mmc expert, but, Isn't this sequence part of the programmer
manual in the TRM[1]? Either way, one additional issue I did end up with
when I was doing beagleplay[2] was when i booted off emmc and runtime PM
disabled SD/MMC interface, the MMC IP's CD mode would'nt work since the
IP isn't clocked. So I switched the mux mode to GPIO to use mmc CD
there. I haven't timed that approach where
SDHCI_AM654_QUIRK_FORCE_CDTEST would get set.

[1] https://www.ti.com/lit/pdf/spruiv7
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/ti/k3-am625-beagleplay.dts#n835
-- 
Regards,
Nishanth Menon
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