Messages in this thread | | | Subject | Re: [PATCH v2 1/2] mwifiex: Use non-posted PCI write when setting TX ring write pointer | From | Jonas Dreßler <> | Date | Wed, 22 Sep 2021 14:08:39 +0200 |
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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 might be outdated when setting the TX ready interrupt, leading to 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@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 + * interrupt but the TX ring write pointer points to an outdated 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. >
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.
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