linux-kernel - Re: [PATCH 0/2] mmc: sdhci: add quirk to disable bounce buffer

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Message-ID: <a9934d68-8b8f-49b8-b4a3-053e3949c666@intel.com>
Date: Mon, 6 Oct 2025 10:35:35 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Michael Garofalo <officialtechflashyt@...il.com>, <ulf.hansson@...aro.org>
CC: <linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] mmc: sdhci: add quirk to disable bounce buffer

On 06/10/2025 04:36, Michael Garofalo wrote:
> This patch series adds a new bit to quirks2 for disabling the bounce
> buffer.  On some hardware, this is required for proper operation.  An
> example of such hardware is the SDHCI controller of the Nintendo Wii's
> "Hollywood" chipset.  Without this patch, the onboard Broadcom 4318
> Wi-Fi fails to connect to any networks.

The bounce buffer should not make any difference, so it is likely
a different problem that gets hidden when the bounce buffer is not
used.

Could you enable dynamic debug messages and show the messages
for the failing case?

Dynamic debug for mmc
---------------------

    Kernel must be configured:

        CONFIG_DYNAMIC_DEBUG=y

    To enable mmc debug via sysfs:

        echo 'file drivers/mmc/core/* +p' > /sys/kernel/debug/dynamic_debug/control
        echo 'file drivers/mmc/host/* +p' > /sys/kernel/debug/dynamic_debug/control

    To enable mmc debug via kernel command line:

        dyndbg="file drivers/mmc/core/* +p;file drivers/mmc/host/* +p"

    To disable mmc debug:

        echo 'file drivers/mmc/core/* -p' > /sys/kernel/debug/dynamic_debug/control
        echo 'file drivers/mmc/host/* -p' > /sys/kernel/debug/dynamic_debug/control

    More general information in kernel documentation in kernel tree:

        Documentation/admin-guide/dynamic-debug-howto.rst
	https://www.kernel.org/doc/html/latest/admin-guide/dynamic-debug-howto.html


> 
> Patch 1 introduces the new quirk bit.
> Patch 2 applies it to sdhci-of-hlwd.
> 
> Michael Garofalo (2):
>   mmc: sdhci: add quirk to disable the bounce buffer
>   mmc: sdhci-of-hlwd: disable bounce buffer usage
> 
>  drivers/mmc/host/sdhci-of-hlwd.c | 1 +
>  drivers/mmc/host/sdhci.c         | 8 +++++---
>  drivers/mmc/host/sdhci.h         | 4 ++++
>  3 files changed, 10 insertions(+), 3 deletions(-)
>