Am Wed, 11 Apr 2018 13:33:02 -0300 schrieb Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>: > Em Wed, 11 Apr 2018 18:03:15 +0200 > Daniel Scheller <d.scheller.oss@xxxxxxxxx> escreveu: > > > Am Wed, 11 Apr 2018 08:03:37 -0400 > > schrieb Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>: > > > > > Currently, ddbridge produces 4 warnings on sparse: > > > drivers/media/pci/ddbridge/ddbridge-core.c:495:9: warning: context imbalance in 'ddb_output_start' - different lock contexts for basic block > > > drivers/media/pci/ddbridge/ddbridge-core.c:510:9: warning: context imbalance in 'ddb_output_stop' - different lock contexts for basic block > > > drivers/media/pci/ddbridge/ddbridge-core.c:525:9: warning: context imbalance in 'ddb_input_stop' - different lock contexts for basic block > > > drivers/media/pci/ddbridge/ddbridge-core.c:560:9: warning: context imbalance in 'ddb_input_start' - different lock contexts for basic block > > > > > > Those are all false positives, but they result from the fact that > > > there could potentially have some troubles at the locking schema, > > > because the lock depends on a var (output->dma). > > > > > > I discussed that in priv with Sparse author and with the current > > > maintainer. Both believe that sparse is doing the right thing, and > > > that the proper fix would be to change the code to make it clearer > > > that, when spin_lock_irq() is called, spin_unlock_irq() will be > > > also called. > > > > > > That help not only static analyzers to better understand the code, > > > but also humans that could need to take a look at the code. > > > > > > It was also pointed that gcc would likely be smart enough to > > > optimize the code and produce the same result. I double > > > checked: indeed, the size of the driver didn't change after > > > this patch. > > > > > > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx> > > > --- > > > drivers/media/pci/ddbridge/ddbridge-core.c | 43 ++++++++++++++++++++---------- > > > 1 file changed, 29 insertions(+), 14 deletions(-) > > > > > > diff --git a/drivers/media/pci/ddbridge/ddbridge-core.c b/drivers/media/pci/ddbridge/ddbridge-core.c > > > index 4a2819d3e225..080e2189ca7f 100644 > > > --- a/drivers/media/pci/ddbridge/ddbridge-core.c > > > +++ b/drivers/media/pci/ddbridge/ddbridge-core.c > > > @@ -458,13 +458,12 @@ static void calc_con(struct ddb_output *output, u32 *con, u32 *con2, u32 flags) > > > *con2 = (nco << 16) | gap; > > > } > > > > > > -static void ddb_output_start(struct ddb_output *output) > > > +static void __ddb_output_start(struct ddb_output *output) > > > { > > > struct ddb *dev = output->port->dev; > > > u32 con = 0x11c, con2 = 0; > > > > > > if (output->dma) { > > > - spin_lock_irq(&output->dma->lock); > > > output->dma->cbuf = 0; > > > output->dma->coff = 0; > > > output->dma->stat = 0; > > > @@ -492,9 +491,18 @@ static void ddb_output_start(struct ddb_output *output) > > > > > > ddbwritel(dev, con | 1, TS_CONTROL(output)); > > > > > > - if (output->dma) { > > > + if (output->dma) > > > output->dma->running = 1; > > > +} > > > + > > > +static void ddb_output_start(struct ddb_output *output) > > > +{ > > > + if (output->dma) { > > > + spin_lock_irq(&output->dma->lock); > > > + __ddb_output_start(output); > > > spin_unlock_irq(&output->dma->lock); > > > + } else { > > > + __ddb_output_start(output); > > > } > > > } > > > > This makes things look rather strange (at least to my eyes), especially > > when simply trying to satisfy automated checkers, which in this case is > > useless since both lock and unlock will always happen based on the same > > condition ([input|output]->dma != NULL). Though I agree having the > > locking inside a condition in it's current form isn't optimal, too, and > > I also already thought about this in the past. > > > > I'd rather try to fix this by checking for the dma ptrs at the > > beginning of the four functions and immediately return if the ptr is > > invalid. Though I don't know if this may cause side effects as there's > > data written to the regs pointed by the TS_CONTROL() macros even if > > there's no dma ptr present. > > > > I'd like to hear Ralph's opinion on this, and also like to have this > > changed (in whatever way) in the upstream (dddvb) repository, too. > > > > Please refrain from applying this patch until we agreed on a proper > > solution that works for everyone. > > Yeah, sure. > > Btw, does ddbridge driver works without DMA? On a quick look, it > seems that it is enabled all the times. DMA (and only this way of transportation) is used for all TS stream input/output from/to demods and CI adapters (and the modulator cards in the upstream driver) when driven by any of the PCIe bridges. After another quick glance, [in|out]put->dma should really always be set. In the end, they are pointers to "struct ddb_dma"'s to the fixed members of struct ddb, which is allocated when the driver is loaded via ddb_probe() in ddbridge-main. Not sure at the moment where the assignment to in/output can fail, but if it did, I believe programming the remaining things in the hardware can rather safely be left out aswell. Best regards, Daniel Scheller -- https://github.com/herrnst