linux-kernel - Re: [RFC PATCH 2/9] apple-gmux: consolidate version reading

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Message-ID: <f4992ffa-68db-7f8c-b92d-a0e1348a7839@redhat.com>
Date:   Fri, 10 Feb 2023 20:41:19 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Orlando Chamberlain <orlandoch.dev@...il.com>,
        platform-driver-x86@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Gross <markgross@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Hawking Zhang <Hawking.Zhang@....com>,
        Andrey Grodzovsky <andrey.grodzovsky@....com>,
        Lijo Lazar <lijo.lazar@....com>,
        YiPeng Chai <YiPeng.Chai@....com>,
        Somalapuram Amaranath <Amaranath.Somalapuram@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Bokun Zhang <Bokun.Zhang@....com>,
        Jack Xiao <Jack.Xiao@....com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Rander Wang <rander.wang@...el.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Amadeusz Sławiński 
        <amadeuszx.slawinski@...ux.intel.com>,
        Yong Zhi <yong.zhi@...el.com>, Evan Quan <evan.quan@....com>,
        Kerem Karabay <kekrby@...il.com>,
        Aditya Garg <gargaditya08@...e.com>,
        Aun-Ali Zaidi <admin@...eit.net>
Subject: Re: [RFC PATCH 2/9] apple-gmux: consolidate version reading

Hi,

On 2/10/23 05:48, Orlando Chamberlain wrote:
> Read gmux version in one go as 32 bits on both indexed and classic
> gmux's.
> 
> Classic gmux's used to read the version as
> 
> major = inb(base + 0x4);
> minor = inb(base + 0x5);
> release = inb(base + 0x6);
> 
> but this can instead be done the same way as indexed gmux's with
> gmux_read32(), so the same version reading code is used for classic
> and indexed gmux's (as well as mmio gmux's that will be added to this
> driver).
> 
> Signed-off-by: Orlando Chamberlain <orlandoch.dev@...il.com>
> ---
>  drivers/platform/x86/apple-gmux.c | 14 ++++++--------
>  include/linux/apple-gmux.h        |  6 +-----
>  2 files changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
> index e8cb084cb81f..67628104f31a 100644
> --- a/drivers/platform/x86/apple-gmux.c
> +++ b/drivers/platform/x86/apple-gmux.c
> @@ -580,15 +580,13 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
>  	if (indexed) {
>  		mutex_init(&gmux_data->index_lock);
>  		gmux_data->indexed = true;
> -		version = gmux_read32(gmux_data, GMUX_PORT_VERSION_MAJOR);
> -		ver_major = (version >> 24) & 0xff;
> -		ver_minor = (version >> 16) & 0xff;
> -		ver_release = (version >> 8) & 0xff;
> -	} else {
> -		ver_major = gmux_read8(gmux_data, GMUX_PORT_VERSION_MAJOR);
> -		ver_minor = gmux_read8(gmux_data, GMUX_PORT_VERSION_MINOR);
> -		ver_release = gmux_read8(gmux_data, GMUX_PORT_VERSION_RELEASE);
>  	}
> +
> +	version = gmux_read32(gmux_data, GMUX_PORT_VERSION_MAJOR);
> +	ver_major = (version >> 24) & 0xff;
> +	ver_minor = (version >> 16) & 0xff;
> +	ver_release = (version >> 8) & 0xff;
> +
>  	pr_info("Found gmux version %d.%d.%d [%s]\n", ver_major, ver_minor,
>  		ver_release, (gmux_data->indexed ? "indexed" : "classic"));
>  

The problem with this is that there is nothing (no known register)
at address base + 7 and now you are reading from address base + 7
here where before the code was not, we have no idea how the hw
will respond to this.  This should be pretty innocent but still ...

> diff --git a/include/linux/apple-gmux.h b/include/linux/apple-gmux.h
> index 1f68b49bcd68..eb2caee04abd 100644
> --- a/include/linux/apple-gmux.h
> +++ b/include/linux/apple-gmux.h
> @@ -67,7 +67,6 @@ static inline bool apple_gmux_is_indexed(unsigned long iostart)
>   */
>  static inline bool apple_gmux_detect(struct pnp_dev *pnp_dev, bool *indexed_ret)
>  {
> -	u8 ver_major, ver_minor, ver_release;
>  	struct device *dev = NULL;
>  	struct acpi_device *adev;
>  	struct resource *res;
> @@ -95,10 +94,7 @@ static inline bool apple_gmux_detect(struct pnp_dev *pnp_dev, bool *indexed_ret)
>  	 * Invalid version information may indicate either that the gmux
>  	 * device isn't present or that it's a new one that uses indexed io.
>  	 */
> -	ver_major = inb(res->start + GMUX_PORT_VERSION_MAJOR);
> -	ver_minor = inb(res->start + GMUX_PORT_VERSION_MINOR);
> -	ver_release = inb(res->start + GMUX_PORT_VERSION_RELEASE);
> -	if (ver_major == 0xff && ver_minor == 0xff && ver_release == 0xff) {
> +	if (!(~inl(res->start + GMUX_PORT_VERSION_MAJOR))) {

Assuming we can get this tested well enough that I'm ok with the change in general
please write this as:

	if (inl(res->start + GMUX_PORT_VERSION_MAJOR) == 0xffffffff) {

Which I believe is what you are trying to achieve here ?

Regards,

Hans



>  		indexed = apple_gmux_is_indexed(res->start);
>  		if (!indexed)
>  			goto out;