linux-kernel - Re: [RFC PATCH 1/9] apple-gmux: use cpu_to

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Date:   Fri, 10 Feb 2023 20:33:26 +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 1/9] apple-gmux: use cpu_to_be32 instead of manual
 reorder

Hi,

On 2/10/23 20:09, Hans de Goede wrote:
> Hi,
> 
> On 2/10/23 05:48, Orlando Chamberlain wrote:
>> Currently it manually flips the byte order, but we can instead use
>> cpu_to_be32(val) for this.
>>
>> Signed-off-by: Orlando Chamberlain <orlandoch.dev@...il.com>
>> ---
>>  drivers/platform/x86/apple-gmux.c | 18 ++----------------
>>  1 file changed, 2 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
>> index 9333f82cfa8a..e8cb084cb81f 100644
>> --- a/drivers/platform/x86/apple-gmux.c
>> +++ b/drivers/platform/x86/apple-gmux.c
>> @@ -94,13 +94,7 @@ static u32 gmux_pio_read32(struct apple_gmux_data *gmux_data, int port)
>>  static void gmux_pio_write32(struct apple_gmux_data *gmux_data, int port,
>>  			     u32 val)
>>  {
>> -	int i;
>> -	u8 tmpval;
>> -
>> -	for (i = 0; i < 4; i++) {
>> -		tmpval = (val >> (i * 8)) & 0xff;
>> -		outb(tmpval, gmux_data->iostart + port + i);
>> -	}
>> +	outl(cpu_to_be32(val), gmux_data->iostart + port);
>>  }
>>  
>>  static int gmux_index_wait_ready(struct apple_gmux_data *gmux_data)
> 
> The ioport / indexed-ioport accessed apple_gmux-es likely are (part of?)
> LPC bus devices . Looking at the bus level you are now changing 4 io
> accesses with a size of 1 byte, to 1 32 bit io-access.

Correction to myself, re-reading the LPC specification, then
if I'm right and this is a LPC device then all IO in/out accesses
are always 1 byte accesses. Since the LPC bus only supports 16 / 32
bit accesses for DMA cycles.

So presumably the outl() would get split into 4 separate 8 bit
(port) IO accesses.

Regards,

Hans





>> @@ -177,16 +171,8 @@ static u32 gmux_index_read32(struct apple_gmux_data *gmux_data, int port)
>>  static void gmux_index_write32(struct apple_gmux_data *gmux_data, int port,
>>  			       u32 val)
>>  {
>> -	int i;
>> -	u8 tmpval;
>> -
>>  	mutex_lock(&gmux_data->index_lock);
>> -
>> -	for (i = 0; i < 4; i++) {
>> -		tmpval = (val >> (i * 8)) & 0xff;
>> -		outb(tmpval, gmux_data->iostart + GMUX_PORT_VALUE + i);
>> -	}
>> -
>> +	outl(cpu_to_be32(val), gmux_data->iostart + GMUX_PORT_VALUE);
>>  	gmux_index_wait_ready(gmux_data);
>>  	outb(port & 0xff, gmux_data->iostart + GMUX_PORT_WRITE);
>>  	gmux_index_wait_complete(gmux_data);
>