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Date: Sat, 11 Feb 2023 10:30:24 +1100
From: Orlando Chamberlain <orlandoch.dev@...il.com>
To: Hans de Goede <hdegoede@...hat.com>
Cc: platform-driver-x86@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
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
On Fri, 10 Feb 2023 20:19:27 +0100
Hans de Goede <hdegoede@...hat.com> wrote:
> 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.
> >
> > 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.
>
> A quick follow up on this, I just noticed that only the pio_write32
> is doing the one byte at a time thing:
>
> static u32 gmux_pio_read32(struct apple_gmux_data *gmux_data, int
> port) {
> return inl(gmux_data->iostart + 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);
> }
> }
>
> And if you look closely gmux_pio_write32() is not swapping
> the order to be32 at all, it is just taking the bytes
> in little-endian memory order, starting with the first
> (index 0) byte which is the least significant byte of
> the value.
>
> On x86 the original code is no different then doing:
>
> static void gmux_pio_write32(struct apple_gmux_data *gmux_data, int
> port, u32 val)
> {
> u8 *data = (u8 *)&val;
> int i;
>
> for (i = 0; i < 4; i++)
> outb(data[i], gmux_data->iostart + port + i);
> }
>
> So yeah this patch is definitely wrong, it actually swaps
> the byte order compared to the original code. Which becomes
> clear when you look the weird difference between the read32 and
> write32 functions after this patch.
>
> Presumably there is a specific reason why gmux_pio_write32()
> is not already doing a single outl(..., val) and byte-ordering
> is not the reason.
>
> Regards,
>
> Hans
Sounds like it may be better to just drop this patch as there's very
little benefit for the risk of causing a regression.
>
>
>
> >> @@ -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);
> >
>
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