On Mon, Apr 22, 2024, at 10:34, Niklas Schnelle wrote:
> On Thu, 2024-04-11 at 16:00 +0200, Helge Deller wrote:
>> * Niklas Schnelle <schnelle@xxxxxxxxxxxxx>:
>> > In a future patch HAS_IOPORT=n will disable inb()/outb() and friends at
>> > compile time. We thus need to #ifdef functions and their callsites which
>> > unconditionally use these I/O accessors. In the include/video/vga.h
>> > these are conveniently all those functions with the vga_io_* prefix.
>>
>> Why don't you code it like in the patch below?
>> inb_p(), outb_p() and outw() would then need to be defined externally
>> without an implementation so that they would generate link time errors
>> (instead of compile time errors).
>
> This may be personal preference but I feel like link time errors would
> be very late to catch a configuration that can't work. Also this would
> bypass the __compiletime_error("inb()) requires CONFIG_HAS_IOPORT");
> added instead of the in*()/out*() helpers to make it easy to spot the
> problem.
>
> I'm not a fan of #ifdeffery either but I think in this case it is
> simple, well enough contained and overall there aren't that many spots
> where we need to exclude just some sections of code vs entire drivers
> with vga.h probably being the worst of them all.
Agreed. I also tried to see if we can move stuff out of vga.h
to have it included in fewer places, as almost everything that
uses this header already has a HAS_IOPORT dependency, but that
would be a lot more work.
The other one that gains a few ugly #ifdefs is the 8250 driver,
everything else is already merged in linux-next or needs a simple
Kconfig dependency.
I think we can make the vga.h file a little more readable
by duplicating the functions and still keep the __compiletime_error()
version in asm/io.h, see below.
Arnd
diff --git a/include/video/vga.h b/include/video/vga.h
index 947c0abd04ef..7e1d8252b732 100644
--- a/include/video/vga.h
+++ b/include/video/vga.h
@@ -197,6 +197,23 @@ struct vgastate {
extern int save_vga(struct vgastate *state);
extern int restore_vga(struct vgastate *state);
+static inline unsigned char vga_mm_r (void __iomem *regbase, unsigned short port)
+{
+ return readb (regbase + port);
+}
+
+static inline void vga_mm_w (void __iomem *regbase, unsigned short port, unsigned char val)
+{
+ writeb (val, regbase + port);
+}
+
+static inline void vga_mm_w_fast (void __iomem *regbase, unsigned short port,
+ unsigned char reg, unsigned char val)
+{
+ writew (VGA_OUT16VAL (val, reg), regbase + port);
+}
+
+#ifdef CONFIG_HAS_IOPORT
/*
* generic VGA port read/write
*/
@@ -217,22 +234,6 @@ static inline void vga_io_w_fast (unsigned short port, unsigned char reg,
outw(VGA_OUT16VAL (val, reg), port);
}
-static inline unsigned char vga_mm_r (void __iomem *regbase, unsigned short port)
-{
- return readb (regbase + port);
-}
-
-static inline void vga_mm_w (void __iomem *regbase, unsigned short port, unsigned char val)
-{
- writeb (val, regbase + port);
-}
-
-static inline void vga_mm_w_fast (void __iomem *regbase, unsigned short port,
- unsigned char reg, unsigned char val)
-{
- writew (VGA_OUT16VAL (val, reg), regbase + port);
-}
-
static inline unsigned char vga_r (void __iomem *regbase, unsigned short port)
{
if (regbase)
@@ -258,7 +259,25 @@ static inline void vga_w_fast (void __iomem *regbase, unsigned short port,
else
vga_io_w_fast (port, reg, val);
}
+#else
+static inline unsigned char vga_r (void __iomem *regbase, unsigned short port)
+{
+ return vga_mm_r(regbase, port);
+}
+
+static inline void vga_w(void __iomem *regbase, unsigned short port, unsigned char val)
+{
+ vga_mm_w (regbase, port, val);
+}
+
+static inline void vga_w_fast (void __iomem *regbase, unsigned short port,
+ unsigned char reg, unsigned char val)
+{
+ vga_mm_w_fast(regbase, port, reg, val);
+}
+
+#endif
/*
* VGA CRTC register read/write
