Re: [RFC PATCH 1/9] apple-gmux: use cpu_to_be32 instead of manual reorder

[Hans de Goede <hdegoede@redhat.com>]

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@gmail.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.

Depending on the decoding hw in the chip this may work fine,
or this may work not at all.

I realized that you have asked for more testing, but most surviving
macbooks from the older apple-gmux era appear to be models without
a discrete GPU (which are often the first thing to break) and thus
without a gmux.

Unless we get a bunch of testers to show up, which I doubt. I would
prefer slightly bigger / less pretty code and not change the functional
behavior of the driver on these older models.

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);