On 9/22/21 1:17 PM, Andy Shevchenko wrote:
On Tue, Sep 14, 2021 at 01:48:12PM +0200, Jonas Dreßler wrote:
On the 88W8897 card it's very important the TX ring write pointer is
updated correctly to its new value before setting the TX ready
interrupt, otherwise the firmware appears to crash (probably because
it's trying to DMA-read from the wrong place). The issue is present in
the latest firmware version 15.68.19.p21 of the pcie+usb card.
Please, be consistent in the commit message(s) and the code (esp. if the term
comes from a specification).
Here, PCIe (same in the code, at least that I have noticed, but should be done
everywhere).
Since PCI uses "posted writes" when writing to a register, it's not
guaranteed that a write will happen immediately. That means the pointer
might be outdated when setting the TX ready interrupt, leading to
firmware crashes especially when ASPM L1 and L1 substates are enabled
(because of the higher link latency, the write will probably take
longer).
So fix those firmware crashes by always using a non-posted write for
this specific register write. We do that by simply reading back the
register after writing it, just as a few other PCI drivers do.
This fixes a bug where during rx/tx traffic and with ASPM L1 substates
Ditto. TX/RX.
enabled (the enabled substates are platform dependent), the firmware
crashes and eventually a command timeout appears in the logs.
Should it have a Fixes tag?
Don't think so, there's the infamous
(https://bugzilla.kernel.org/show_bug.cgi?id=109681) Bugzilla bug it
fixes though, I'll mention that in v3.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jonas Dreßler <verdre@xxxxxxx>
...
- /* Write the TX ring write pointer in to reg->tx_wrptr */
- if (mwifiex_write_reg(adapter, reg->tx_wrptr,
- card->txbd_wrptr | rx_val)) {
+ /* Write the TX ring write pointer in to reg->tx_wrptr.
+ * The firmware (latest version 15.68.19.p21) of the 88W8897
+ * pcie+usb card seems to crash when getting the TX ready
+ * interrupt but the TX ring write pointer points to an outdated
+ * address, so it's important we do a non-posted write here to
+ * force the completion of the write.
+ */
+ if (mwifiex_write_reg_np(adapter, reg->tx_wrptr,
+ card->txbd_wrptr | rx_val)) {
mwifiex_dbg(adapter, ERROR,
"SEND DATA: failed to write reg->tx_wrptr\n");
ret = -1;
I'm not sure how this is not a dead code.
On top of that, I would rather to call old function and explicitly put the
dummy read after it
/* Write the TX ring write pointer in to reg->tx_wrptr */
if (mwifiex_write_reg(adapter, reg->tx_wrptr,
card->txbd_wrptr | rx_val)) {
...eliminate dead code in the following patch(es)...
}
+ /* The firmware (latest version 15.68.19.p21) of the 88W8897
+ * pcie+usb card seems to crash when getting the TX ready
+ * interrupt but the TX ring write pointer points to an outdated
+ * address, so it's important we do a non-posted write here to
+ * force the completion of the write.
+ */
mwifiex_read_reg(...);
Now, since I found the dummy read function to be present, perhaps you need to
dive more into the code and understand why it exists.
Interesting, I haven't noticed that mwifiex_write_reg() always returns
0. So are you suggesting to remove that return value and get rid of all
the "if (mwifiex_write_reg()) {}" checks in a separate commit?
As for why the dummy read/write functions exist, I have no idea. Looking
at git history it seems they were always there (only change is that
mwifiex_read_reg() started to handle read errors with commit
af05148392f50490c662dccee6c502d9fcba33e2). My bet would be that they
were created to be consistent with sdio.c which is the oldest supported
bus type in mwifiex.
