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Message-ID: <20160826113848.GO1041@n2100.armlinux.org.uk>
Date: Fri, 26 Aug 2016 12:38:48 +0100
From: Russell King - ARM Linux <linux@...linux.org.uk>
To: Arnd Bergmann <arnd@...db.de>
Cc: linux-arm-kernel@...ts.infradead.org,
Robert Jarzmik <robert.jarzmik@...e.fr>,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
Nicolas Pitre <nico@...xnic.net>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] smc91x: remove ARM hack for unaligned 16-bit writes
On Fri, Aug 26, 2016 at 11:41:21AM +0200, Arnd Bergmann wrote:
> On Thursday, August 25, 2016 11:37:43 PM CEST Russell King - ARM Linux wrote:
> > On Thu, Aug 25, 2016 at 08:02:35PM +0200, Robert Jarzmik wrote:
> > > Arnd Bergmann <arnd@...db.de> writes:
> > /*
> > + * Any 16-bit access is performed with two 8-bit accesses if the hardware
> > + * can't do it directly. Most registers are 16-bit so those are mandatory.
> > + */
> > +#define SMC_outw_b(x, a, r) \
> > + do { \
> > + unsigned int __val16 = (x); \
> > + unsigned int __reg = (r); \
> > + SMC_outb(__val16, a, __reg); \
> > + SMC_outb(__val16 >> 8, a, __reg + (1 << SMC_IO_SHIFT)); \
> > + } while (0)
> > +
> > +#define SMC_inw_b(a, r) \
> > + ({ \
> > + unsigned int __val16; \
> > + unsigned int __reg = r; \
> > + __val16 = SMC_inb(a, __reg); \
> > + __val16 |= SMC_inb(a, __reg + (1 << SMC_IO_SHIFT)) << 8; \
> > + __val16; \
> > + })
> > +
> > +/*
> > * Define your architecture specific bus configuration parameters here.
> > */
> >
> > @@ -55,10 +76,30 @@
> > #define SMC_IO_SHIFT (lp->io_shift)
> >
> > #define SMC_inb(a, r) readb((a) + (r))
> > -#define SMC_inw(a, r) readw((a) + (r))
> > +#define SMC_inw(a, r) \
> > + ({ \
> > + unsigned int __smc_r = r; \
> > + SMC_16BIT(lp) ? readw((a) + __smc_r) : \
> > + SMC_8BIT(lp) ? SMC_inw_b(a, __smc_r) : \
> > + ({ BUG(); 0; }); \
> > + })
> > +
>
> I think this breaks machines that declare a device that just lists
> SMC91X_USE_32BIT but not SMC91X_USE_16BIT. Right now, the way this
> is interpreted is to use 32-bit accessors for most things, but
> not avoiding 16-bit reads.
Your comment is wrong. It breaks machines that declare a device
with SMC91X_USE_32BIT but not _either_ of SMC91X_USE_16BIT _or_
SMC91X_USE_8BIT. As I already noted, but you obviously ignored.
In that note, I pointed out that this _was_ already the case with
the original driver before your patch:
#if ! SMC_CAN_USE_16BIT
... code implementing SMC_outw() and SMC_inw() in terms of SMC_outb()
and SMC_inb(), and defining SMC_insw() and SMC_outsw() as BUG()
#endif
#if !defined(SMC_insw) || !defined(SMC_outsw)
#define SMC_insw(a, r, p, l) BUG()
#define SMC_outsw(a, r, p, l) BUG()
#endif
#if ! SMC_CAN_USE_8BIT
#define SMC_inb(ioaddr, reg) ({ BUG(); 0; })
#define SMC_outb(x, ioaddr, reg) BUG()
#define SMC_insb(a, r, p, l) BUG()
#define SMC_outsb(a, r, p, l) BUG()
#endif
#if !defined(SMC_insb) || !defined(SMC_outsb)
#define SMC_insb(a, r, p, l) BUG()
#define SMC_outsb(a, r, p, l) BUG()
#endif
So, if _neither_ SMC_CAN_USE_16BIT nor SMC_CAN_USE_8BIT are defined,
trying to use the 16-bit accessors cause a BUG().
> That is a bit fishy though, and we could instead change the platform
> data to always set both SMC91X_USE_32BIT and SMC91X_USE_16BIT.
>
> The affected platforms are DT based machines with 32-bit I/O and
> these board files:
>
> arch/arm/mach-pxa/idp.c: .flags = SMC91X_USE_32BIT | SMC91X_USE_DMA | SMC91X_NOWAIT,
> arch/arm/mach-pxa/xcep.c: .flags = SMC91X_USE_32BIT | SMC91X_NOWAIT | SMC91X_USE_DMA,
> arch/arm/mach-realview/core.c: .flags = SMC91X_USE_32BIT | SMC91X_NOWAIT,
> arch/blackfin/mach-bf561/boards/cm_bf561.c: .flags = SMC91X_USE_32BIT | SMC91X_NOWAIT,
> arch/blackfin/mach-bf561/boards/ezkit.c: .flags = SMC91X_USE_32BIT | SMC91X_NOWAIT,
Right, this looks like another one of your bugs in this conversion.
#elif defined(CONFIG_ARCH_INNOKOM) || \
defined(CONFIG_ARCH_PXA_IDP) || \
defined(CONFIG_ARCH_RAMSES) || \
defined(CONFIG_ARCH_PCM027)
#define SMC_CAN_USE_8BIT 1
#define SMC_CAN_USE_16BIT 1
#define SMC_CAN_USE_32BIT 1
So, IDP can use all of 32-bit, 16-bit and 8-bit accesses, meanwhile your
conversion is telling the driver that it can only use 32-bit => your
conversion of IDP is broken.
Before your conversion, realview depended on the default settings of
smc91x, which is again:
#define SMC_CAN_USE_8BIT 1
#define SMC_CAN_USE_16BIT 1
#define SMC_CAN_USE_32BIT 1
So realview follows IDP - it can do 32-bit, 16-bit and 8-bit accesses,
meanwhile your conversion tells the driver it can _only_ do 32-bit
accesses, which is again broken.
XCEP falls into the same category, as do the other two blackfin
cases from what I can see.
The point of the SMC_CAN_USE_xxx macros is to indicate to the SMC91x
driver which sizes of access can be used on the hardware concerned.
If SMC_CAN_USE_16BIT is set, then 16-bit accesses are possible. If
it's not set, then 8-bit accesses will be used if they're supported,
otherwise it's a buggy configuration.
SMC_CAN_USE_32BIT says that 32-bit accesses are possible, but these
are only used in a small number of cases as an optimisation.
It is a bug to configure the smc91x driver with both SMC_CAN_USE_16BIT
and SMC_CAN_USE_8BIT clear.
Hence, it's a bug to tell the driver (via the platform data) that only
32-bit accesses can be performed.
So, while my patch may be fixing some of the brokenness, the rest of
the brokenness also needs fixing by adjusting all the platform data
to properly reflect which access sizes are possible, rather than what
you seem to have done, which is to indicate what the largest possible
access size is.
This is especially important as there are platforms around where 16-bit
accesses to the SMC91x can be performed, but not 8-bit:
#elif defined(CONFIG_MACH_LOGICPD_PXA270) || \
defined(CONFIG_MACH_NOMADIK_8815NHK)
#define SMC_CAN_USE_8BIT 0
#define SMC_CAN_USE_16BIT 1
#define SMC_CAN_USE_32BIT 0
#elif defined(CONFIG_SH_SH4202_MICRODEV)
#define SMC_CAN_USE_8BIT 0
#define SMC_CAN_USE_16BIT 1
#define SMC_CAN_USE_32BIT 0
#elif defined(CONFIG_M32R)
#define SMC_CAN_USE_8BIT 0
#define SMC_CAN_USE_16BIT 1
#define SMC_CAN_USE_32BIT 0
#elif defined(CONFIG_ARCH_MSM)
#define SMC_CAN_USE_8BIT 0
#define SMC_CAN_USE_16BIT 1
#define SMC_CAN_USE_32BIT 0
#elif defined(CONFIG_COLDFIRE)
#define SMC_CAN_USE_8BIT 0
#define SMC_CAN_USE_16BIT 1
#define SMC_CAN_USE_32BIT 0
... etc ...
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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