linux-kernel - Re: [PATCH v8 3/5] drm: handle HAS

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Message-Id: <a25086c4-e2fc-4ffc-bc20-afa50e560d96@app.fastmail.com>
Date: Mon, 21 Oct 2024 10:08:19 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Thomas Zimmermann" <tzimmermann@...e.de>,
 "Niklas Schnelle" <schnelle@...ux.ibm.com>, "Brian Cain" <bcain@...cinc.com>,
 "Marcel Holtmann" <marcel@...tmann.org>,
 "Luiz Augusto von Dentz" <luiz.dentz@...il.com>,
 "Patrik Jakobsson" <patrik.r.jakobsson@...il.com>,
 "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
 "Maxime Ripard" <mripard@...nel.org>, "Dave Airlie" <airlied@...il.com>,
 "Simona Vetter" <simona@...ll.ch>, "Dave Airlie" <airlied@...hat.com>,
 "Gerd Hoffmann" <kraxel@...hat.com>,
 "Lucas De Marchi" <lucas.demarchi@...el.com>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 "Rodrigo Vivi" <rodrigo.vivi@...el.com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Jiri Slaby" <jirislaby@...nel.org>, "Maciej W. Rozycki" <macro@...am.me.uk>,
 "Heiko Carstens" <hca@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-hexagon@...r.kernel.org,
 linux-bluetooth@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 virtualization@...ts.linux.dev, spice-devel@...ts.freedesktop.org,
 intel-xe@...ts.freedesktop.org, linux-serial@...r.kernel.org,
 Linux-Arch <linux-arch@...r.kernel.org>, "Arnd Bergmann" <arnd@...nel.org>
Subject: Re: [PATCH v8 3/5] drm: handle HAS_IOPORT dependencies

On Mon, Oct 21, 2024, at 07:52, Thomas Zimmermann wrote:
> Am 08.10.24 um 14:39 schrieb Niklas Schnelle:
d 100644
>> --- a/drivers/gpu/drm/qxl/Kconfig
>> +++ b/drivers/gpu/drm/qxl/Kconfig
>> @@ -2,6 +2,7 @@
>>   config DRM_QXL
>>   	tristate "QXL virtual GPU"
>>   	depends on DRM && PCI && MMU
>> +	depends on HAS_IOPORT
>
> Is there a difference between this style (multiple 'depends on') and the 
> one used for gma500 (&& && &&)?

No, it's the same. Doing it in one line is mainly useful
if you have some '||' as well.

>> @@ -105,7 +106,9 @@ static void bochs_vga_writeb(struct bochs_device *bochs, u16 ioport, u8 val)
>>   
>>   		writeb(val, bochs->mmio + offset);
>>   	} else {
>> +#ifdef CONFIG_HAS_IOPORT
>>   		outb(val, ioport);
>> +#endif
>
> Could you provide empty defines for the out() interfaces at the top of 
> the file?

That no longer works since there are now __compiletime_error()
versions of these funcitons. However we can do it more nicely like:

diff --git a/drivers/gpu/drm/tiny/bochs.c b/drivers/gpu/drm/tiny/bochs.c
index 9b337f948434..034af6e32200 100644
--- a/drivers/gpu/drm/tiny/bochs.c
+++ b/drivers/gpu/drm/tiny/bochs.c
@@ -112,14 +112,12 @@ static void bochs_vga_writeb(struct bochs_device *bochs, u16 ioport, u8 val)
 	if (WARN_ON(ioport < 0x3c0 || ioport > 0x3df))
 		return;

-	if (bochs->mmio) {
+	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
 		int offset = ioport - 0x3c0 + 0x400;

 		writeb(val, bochs->mmio + offset);
 	} else {
-#ifdef CONFIG_HAS_IOPORT
 		outb(val, ioport);
-#endif
 	}
 }

@@ -128,16 +126,12 @@ static u8 bochs_vga_readb(struct bochs_device *bochs, u16 ioport)
 	if (WARN_ON(ioport < 0x3c0 || ioport > 0x3df))
 		return 0xff;

-	if (bochs->mmio) {
+	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
 		int offset = ioport - 0x3c0 + 0x400;

 		return readb(bochs->mmio + offset);
 	} else {
-#ifdef CONFIG_HAS_IOPORT
 		return inb(ioport);
-#else
-		return 0xff;
-#endif
 	}
 }

@@ -145,32 +139,26 @@ static u16 bochs_dispi_read(struct bochs_device *bochs, u16 reg)
 {
 	u16 ret = 0;

-	if (bochs->mmio) {
+	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
 		int offset = 0x500 + (reg << 1);

 		ret = readw(bochs->mmio + offset);
 	} else {
-#ifdef CONFIG_HAS_IOPORT
 		outw(reg, VBE_DISPI_IOPORT_INDEX);
 		ret = inw(VBE_DISPI_IOPORT_DATA);
-#else
-		ret = 0xffff;
-#endif
 	}
 	return ret;
 }

 static void bochs_dispi_write(struct bochs_device *bochs, u16 reg, u16 val)
 {
-	if (bochs->mmio) {
+	if (!IS_DEFINED(CONFIG_HAS_IOPORT) || bochs->mmio) {
 		int offset = 0x500 + (reg << 1);

 		writew(val, bochs->mmio + offset);
 	} else {
-#ifdef CONFIG_HAS_IOPORT
 		outw(reg, VBE_DISPI_IOPORT_INDEX);
 		outw(val, VBE_DISPI_IOPORT_DATA);
-#endif
 	}
 }

> And the in() interfaces could be defined to 0xff[ff].
>
> I assume that you don't want to provide such empty macros in the 
> kernel's io.h header?

That was the original idea many years ago, but Linus rejected
my pull request for it, so Niklas worked through all drivers
individually to add the dependencies instead.

     Arnd