Re: [PATCH] x86/calgary: fix bitcast type warnings

From: Mukesh Ojha
Date: Sat Mar 30 2019 - 06:24:47 EST



On 3/30/2019 3:15 AM, Jann Horn wrote:
On Fri, Mar 29, 2019 at 9:19 AM Mukesh Ojha <mojha@xxxxxxxxxxxxxx> wrote:
On 3/29/2019 4:29 AM, Jann Horn wrote:
The sparse checker attempts to ensure that all conversions between
fixed-endianness numbers and numbers with native endianness are explicit.
However, the calgary code reads and writes big-endian numbers from/to IO
memory using {read,write}{l,q}(), which return native-endian numbers.

This could be addressed by putting __force casts all over the place, but
that would kind of defeat the point of the warning. Instead, create new
helpers {read,write}{l,q}_be() for big-endian IO that convert from/to
native endianness.

Most of this patch is a straightforward conversion; the following parts
aren't just mechanical replacement:

- ->tar_val is now a native-endian number instead of big-endian
- calioc2_handle_quirks() did `cpu_to_be32(readl(target))` when it
intended to do `be32_to_cpu(readl(target))` (but that has no actual
effects outside of type warnings)

This gets rid of 108 lines of sparse warnings.

Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
---
compile-tested only

arch/x86/kernel/pci-calgary_64.c | 108 ++++++++++++++++++-------------
1 file changed, 64 insertions(+), 44 deletions(-)

diff --git a/arch/x86/kernel/pci-calgary_64.c b/arch/x86/kernel/pci-calgary_64.c
index c70720f61a34..36cd66d940fb 100644
--- a/arch/x86/kernel/pci-calgary_64.c
+++ b/arch/x86/kernel/pci-calgary_64.c
@@ -534,6 +534,26 @@ static inline int is_cal_pci_dev(unsigned short device)
return (is_calgary(device) || is_calioc2(device));
}

Can the existing api's not be used here like iowrite64be/ioread64be/ or
similar variant in "include/asm-generic/io.h"
Given what Logan said, I think it probably makes sense to keep the patch as-is?

Sure go ahead, will have a look at this patch one more time.