re: kern/55485: bwfm @ sdmmc hangs, with some diagnosis

[matthew green <mrg%eterna.com.au@localhost>]

The following reply was made to PR kern/55485; it has been noted by GNATS.

From: matthew green <mrg%eterna.com.au@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
    netbsd-bugs%netbsd.org@localhost
Subject: re: kern/55485: bwfm @ sdmmc hangs, with some diagnosis
Date: Sat, 18 Jul 2020 14:16:56 +1000

 more data.  and some likely less broken behaviour fixes, if not
 a full fix.
 
 with some help from riastradh@ and jmcneill@ i've tracked down
 that when the failure is occuring, the only thing looping is
 an interrupt.  we appear to be in dwc_mmc_exec_command() all
 the time, but kernhist logging shows that we re-enter this
 function many times (one time, 1000 times in 60ms.)
 
 initially, byt checking what bits were set in the
 BWFM_SDPCMD_INTSTATUS register, we determined that there was
 the SDPCMD_INTSTATUS_XMTDATA_AVAIL bit set, which is not used
 by our driver.  then we noticed that the interrupt mask reg
 was set to 0xffffffff, with commented version asking for 2
 bits we are interested in.  this allowed my test case to work
 for about 10x longer than average before failing, and the
 failure mode was less hard-hang of bwfm itself.   eg, when
 i ran 'ifconfig -a', it took 15 seconds, but it did complete,
 and 'ifconfig bwfm down up' restored functionality.  (there
 are 3x5s slow periods here, each accompanied by a 'checksum
 error' message on the console.)
 
 the patch below helps a lot, but there are still stability.
 
 
 .mrg.
 
 
 Index: if_bwfm_sdio.c
 ===================================================================
 RCS file: /cvsroot/src/sys/dev/sdmmc/if_bwfm_sdio.c,v
 retrieving revision 1.19
 diff -p -u -r1.19 if_bwfm_sdio.c
 --- if_bwfm_sdio.c	23 Jun 2020 10:09:33 -0000	1.19
 +++ if_bwfm_sdio.c	18 Jul 2020 04:13:51 -0000
 @@ -505,9 +505,12 @@ bwfm_sdio_attachhook(device_t self)
  		goto err;
  	}
  
 -//	bwfm_sdio_dev_write(sc, SDPCMD_HOSTINTMASK,
 -//	    SDPCMD_INTSTATUS_HMB_SW_MASK | SDPCMD_INTSTATUS_CHIPACTIVE);
 +#if 1
 +	bwfm_sdio_dev_write(sc, SDPCMD_HOSTINTMASK,
 +	    SDPCMD_INTSTATUS_HMB_SW_MASK | SDPCMD_INTSTATUS_CHIPACTIVE);
 +#else
  	bwfm_sdio_dev_write(sc, SDPCMD_HOSTINTMASK, 0xffffffff);
 +#endif
  	bwfm_sdio_write_1(sc, BWFM_SDIO_WATERMARK, 8);
  
  	if (bwfm_chip_sr_capable(bwfm)) {