On 11/9/23 20:00, Andy Shevchenko wrote:
On Thu, Nov 09, 2023 at 03:19:27AM +0000, Jan Bottorff wrote:
When running on a many core ARM64 server, errors were
happening in the ISR that looked like corrupted memory. These
corruptions would fix themselves if small delays were inserted
in the ISR. Errors reported by the driver included "i2c_designware
APMC0D0F:00: i2c_dw_xfer_msg: invalid target address" and
"i2c_designware APMC0D0F:00:controller timed out" during
in-band IPMI SSIF stress tests.
The problem was determined to be memory writes in the driver were not
becoming visible to all cores when execution rapidly shifted between
cores, like when a register write immediately triggers an ISR.
Processors with weak memory ordering, like ARM64, make no
guarantees about the order normal memory writes become globally
visible, unless barrier instructions are used to control ordering.
To solve this, regmap accessor functions configured by this driver
were changed to use non-relaxed forms of the low-level register
access functions, which include a barrier on platforms that require
it. This assures memory writes before a controller register access are
visible to all cores. The community concluded defaulting to correct
operation outweighed defaulting to the small performance gains from
using relaxed access functions. Being a low speed device added weight to
this choice of default register access behavior.
...
v3->v4: add missing changelog
Side note: Usually it's enough to just reply to the patch with the changelog.
...
- *val = swab32(readl_relaxed(dev->base + reg));
+ *val = swab32(readl(dev->base + reg));
- writel_relaxed(swab32(val), dev->base + reg);
+ writel(swab32(val), dev->base + reg);
I'm wondering why ioread32be() / iowrite32be() can't be used here...
Probably it would require to switch entire IO to use ioreadXX() /
iowriteXX() APIs and since we touch all of them (?) may be it makes
sense convert to use them at the same time. Dunno.
I would say cosmetic conversions are better to go to another patch.
For this patch:
Acked-by: Jarkko Nikula <jarkko.nikula@xxxxxxxxxxxxxxx>
