Messages in this thread | | | Date | Wed, 22 Sep 2021 14:17:50 +0300 | From | Andy Shevchenko <> | Subject | Re: [PATCH v2 1/2] mwifiex: Use non-posted PCI write when setting TX ring write pointer |
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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 might be outdated when setting the TX ready interrupt, leading to 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?
> Cc: stable@vger.kernel.org > Signed-off-by: Jonas Dreßler <verdre@v0yd.nl>
...
> - /* 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 + * interrupt but the TX ring write pointer points to an outdated 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.
-- With Best Regards, Andy Shevchenko
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