On Fri, 2024-10-25 at 16:52 +0200, Takashi Iwai wrote: > On Fri, 25 Oct 2024 16:28:42 +0200, > Philipp Stanner wrote: > > > > On Fri, 2024-10-25 at 12:44 +0200, Takashi Iwai wrote: > > > On Fri, 25 Oct 2024 11:26:18 +0200, > > > Philipp Stanner wrote: > > > > > > > > Hi, > > > > > > > > On Thu, 2024-10-24 at 17:55 +0200, Takashi Iwai wrote: > > > > > pcim_intx() tries to restore the INTX_DISABLE bit at removal > > > > > via > > > > > devres, but there is a chance that it restores a wrong value. > > > > > Because the value to be restored is blindly assumed to be the > > > > > negative > > > > > of the enable argument, when a driver calls pcim_intx() > > > > > unnecessarily > > > > > for the already enabled state, it'll restore to the disabled > > > > > state in > > > > > turn. btw following our discussion I think the commit message should then also explicitly state that pcim_intx() is supposed to restore the value before the function itself had been called by that driver for the very first time. > > > > > > > > It depends on how it is called, no? > > > > > > > > // INTx == 1 > > > > pcim_intx(pdev, 0); // old INTx value assumed to be 1 -> > > > > correct > > > > > > > > --- > > > > > > > > // INTx == 0 > > > > pcim_intx(pdev, 0); // old INTx value assumed to be 1 -> wrong > > > > > > > > Maybe it makes sense to replace part of the commit text with > > > > something > > > > like the example above? > > > > > > If it helps better understanding, why not. > > > > > > > > Also, when a driver calls pcim_intx() multiple times with > > > > > different enable argument values, the last one will win no > > > > > matter > > > > > what > > > > > value it is. > > > > > > > > Means > > > > > > > > // INTx == 0 > > > > pcim_intx(pdev, 0); // orig_INTx == 1, INTx == 0 > > > > pcim_intx(pdev, 1); // orig_INTx == 0, INTx == 1 > > > > pcim_intx(pdev, 0); // orig_INTx == 1, INTx == 0 > > > > > > > > So in this example the first call would cause a wrong > > > > orig_INTx, > > > > but > > > > the last call – the one "who will win" – seems to do the right > > > > thing, > > > > dosen't it? > > > > > > Yes and no. The last call wins to write the current value, but > > > shouldn't win for setting the original value. The original value > > > must > > > be recorded only from the first call. > > > > Alright, so you think that pcim_intx() should always restore the > > INTx > > state that existed before the driver was loaded. > > > > > > > This patch addresses those inconsistencies by saving the > > > > > original > > > > > INTX_DISABLE state at the first devres_alloc(); this assures > > > > > that > > > > > the > > > > > original state is restored properly, and the later > > > > > pcim_intx() > > > > > calls > > > > > won't overwrite res->orig_intx any longer. > > > > > > > > > > Fixes: 25216afc9db5 ("PCI: Add managed pcim_intx()") > > > > > > > > That commit is also in 6.11, so we need: > > > > > > > > Cc: stable@xxxxxxxxxxxxxxx # 6.11+ > > > > > > OK. > > > > > > > > Link: https://lore.kernel.org/87v7xk2ps5.wl-tiwai@xxxxxxx > > > > > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> > > > > > --- > > > > > drivers/pci/devres.c | 18 ++++++++++++++---- > > > > > 1 file changed, 14 insertions(+), 4 deletions(-) > > > > > > > > > > diff --git a/drivers/pci/devres.c b/drivers/pci/devres.c > > > > > index b133967faef8..aed3c9a355cb 100644 > > > > > --- a/drivers/pci/devres.c > > > > > +++ b/drivers/pci/devres.c > > > > > @@ -438,8 +438,17 @@ static void pcim_intx_restore(struct > > > > > device > > > > > *dev, void *data) > > > > > __pcim_intx(pdev, res->orig_intx); > > > > > } > > > > > > > > > > -static struct pcim_intx_devres > > > > > *get_or_create_intx_devres(struct > > > > > device *dev) > > > > > +static void save_orig_intx(struct pci_dev *pdev, struct > > > > > pcim_intx_devres *res) > > > > > { > > > > > + u16 pci_command; > > > > > + > > > > > + pci_read_config_word(pdev, PCI_COMMAND, > > > > > &pci_command); > > > > > + res->orig_intx = !(pci_command & > > > > > PCI_COMMAND_INTX_DISABLE); > > > > > +} > > > > > + > > > > > +static struct pcim_intx_devres > > > > > *get_or_create_intx_devres(struct > > > > > pci_dev *pdev) > > > > > +{ > > > > > + struct device *dev = &pdev->dev; > > > > > struct pcim_intx_devres *res; > > > > > > > > > > res = devres_find(dev, pcim_intx_restore, NULL, > > > > > NULL); > > > > > @@ -447,8 +456,10 @@ static struct pcim_intx_devres > > > > > *get_or_create_intx_devres(struct device *dev) > > > > > return res; > > > > > > > > > > res = devres_alloc(pcim_intx_restore, sizeof(*res), > > > > > GFP_KERNEL); > > > > > - if (res) > > > > > + if (res) { > > > > > + save_orig_intx(pdev, res); > > > > > > > > This is not the correct place – get_or_create_intx_devres() > > > > should > > > > get > > > > the resource if it exists, or allocate it if it doesn't, but > > > > its > > > > purpose is not to modify the resource. > > > > > > The behavior of the function makes the implementation a bit > > > harder, > > > because the initialization of res->orig_intx should be done only > > > once > > > at the very first call. > > > > > > > > devres_add(dev, res); > > > > > + } > > > > > > > > > > return res; > > > > > } > > > > > @@ -467,11 +478,10 @@ int pcim_intx(struct pci_dev *pdev, int > > > > > enable) > > > > > { > > > > > struct pcim_intx_devres *res; > > > > > > > > > > - res = get_or_create_intx_devres(&pdev->dev); > > > > > + res = get_or_create_intx_devres(pdev); > > > > > if (!res) > > > > > return -ENOMEM; > > > > > > > > > > - res->orig_intx = !enable; > > > > > > > > Here is the right place to call save_orig_intx(). That way you > > > > also > > > > won't need the new variable struct device *dev above :) > > > > > > The problem is that, at this place, we don't know whether it's a > > > freshly created devres or it's an inherited one. So, we'd need > > > to > > > modify get_or_create_intx_devres() to indicate that it's a new > > > creation. Or, maybe simpler would be rather to flatten > > > get_or_create_intx_devres() into pcim_intx(). It's a small > > > function, > > > and it wouldn't be worsen the readability so much. > > > > That might be the best solution. If it's done that way it should > > include a comment detailing the problem. > > > > Looking at the implementation of pci_intx() before > > 25216afc9db53d85dc648aba8fb7f6d31f2c8731 probably indicates that > > you're > > right: > > > > if (dr && !dr->restore_intx) { > > dr->restore_intx = 1; > > dr->orig_intx = !enable; > > } > > > > > > So they used a boolean to only take the first state. Although that > > still wouldn't have necessarily been the pre-driver INTx state. > > IIRC, this code path is reached only after checking that the INTx > state is changed. Hence "!enable" is assured to be the pre-driver > INTx state in the old code. Oh man. Have those folks never heard of comments :( > > > > > > > > That is, something like below. > > > > > > > > > thanks, > > > > > > Takashi > > > > > > --- a/drivers/pci/devres.c > > > +++ b/drivers/pci/devres.c > > > @@ -438,21 +438,6 @@ static void pcim_intx_restore(struct device > > > *dev, void *data) > > > __pcim_intx(pdev, res->orig_intx); > > > } > > > > > > -static struct pcim_intx_devres *get_or_create_intx_devres(struct > > > device *dev) > > > -{ > > > - struct pcim_intx_devres *res; > > > - > > > - res = devres_find(dev, pcim_intx_restore, NULL, NULL); > > > - if (res) > > > - return res; > > > - > > > - res = devres_alloc(pcim_intx_restore, sizeof(*res), > > > GFP_KERNEL); > > > - if (res) > > > - devres_add(dev, res); > > > - > > > - return res; > > > -} > > > - > > > /** > > > * pcim_intx - managed pci_intx() > > > * @pdev: the PCI device to operate on > > > @@ -466,12 +451,21 @@ static struct pcim_intx_devres > > > *get_or_create_intx_devres(struct device *dev) > > > int pcim_intx(struct pci_dev *pdev, int enable) > > > { > > > struct pcim_intx_devres *res; > > > + struct device *dev = &pdev->dev; > > > + u16 pci_command; > > > > > > - res = get_or_create_intx_devres(&pdev->dev); > > > - if (!res) > > > - return -ENOMEM; > > > + res = devres_find(dev, pcim_intx_restore, NULL, NULL); > > > > sth like: > > > > /* > > * pcim_intx() must only restore the INTx value that existed before > > the > > * driver was loaded, i.e., before it called pcim_intx() for the > > * first time. > > */ > > OK, will add it. > > > > + if (!res) { > > > + res = devres_alloc(pcim_intx_restore, > > > sizeof(*res), > > > GFP_KERNEL); > > > + if (!res) > > > + return -ENOMEM; > > > + > > > + pci_read_config_word(pdev, PCI_COMMAND, > > > &pci_command); > > > + res->orig_intx = !(pci_command & > > > PCI_COMMAND_INTX_DISABLE); > > > + > > > + devres_add(dev, res); > > > + } > > > > > > - res->orig_intx = !enable; > > > __pcim_intx(pdev, enable); > > > > Looks like a good idea to me > > > > The only thing I'm wondering about right now is the following: In > > the > > old days, there was only pci_intx(), which either did devres or > > didn't. > > > > Now you have two functions, pcim_intx() and pci_intx(). > > > > The thing is that the driver could theoretically still intermingle > > them > > and for example call pci_intx() before pcim_intx(), which would > > lead > > the latter to still restore the wrong value. > > > > But that's very unlikely and I'm not sure whether we can do > > something > > about it. > > Right, pcim_intx() assures to restore INTx value back to the moment > it > was called. And that should be enough and consistent behavior. The moment *before* it was called *for the first time*. > > BTW, a possible optimization would be to skip the devres if the value > isn't really changed from the current state (which is similar like > the > old code before pcim_intx()). OTOH, this can lead to inconsistencies > when INTx is changed manually after pcim_intx() somehow. So maybe > it's not worth. There is only a very tiny number of pci{m}_intx() users, they mostly use it in their probe() function, and future use is discouraged in favor of pci_alloc_irq_vectors(). So I think you can save yourself that effort. P. > > > thanks, > > Takashi >