On Tue, Feb 06, 2024 at 10:12:44PM +0530, Ajay Agarwal wrote:
> On Mon, Feb 05, 2024 at 12:52:45AM +0300, Serge Semin wrote:
> > On Sun, Feb 04, 2024 at 04:54:25PM +0530, Ajay Agarwal wrote:
> > > There can be platforms that do not use/have 32-bit DMA addresses
> > > but want to enumerate endpoints which support only 32-bit MSI
> > > address. The current implementation of 32-bit IOVA allocation can
> > > fail for such platforms, eventually leading to the probe failure.
> > >
> > > If there vendor driver has already setup the MSI address using
> > > some mechanism, use the same. This method can be used by the
> > > platforms described above to support EPs they wish to.
> > >
> > > Else, if the memory region is not reserved, try to allocate a
> > > 32-bit IOVA. Additionally, if this allocation also fails, attempt
> > > a 64-bit allocation for probe to be successful. If the 64-bit MSI
> > > address is allocated, then the EPs supporting 32-bit MSI address
> > > will not work.
> > >
> > > Signed-off-by: Ajay Agarwal <ajayagarwal@xxxxxxxxxx>
> > > ---
> > > Changelog since v2:
> > > - If the vendor driver has setup the msi_data, use the same
> > >
> > > Changelog since v1:
> > > - Use reserved memory, if it exists, to setup the MSI data
> > > - Fallback to 64-bit IOVA allocation if 32-bit allocation fails
> > >
> > > .../pci/controller/dwc/pcie-designware-host.c | 26 ++++++++++++++-----
> > > 1 file changed, 20 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > index d5fc31f8345f..512eb2d6591f 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > @@ -374,10 +374,18 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
> > > * order not to miss MSI TLPs from those devices the MSI target
> > > * address has to be within the lowest 4GB.
> > > *
> >
> > > - * Note until there is a better alternative found the reservation is
> > > - * done by allocating from the artificially limited DMA-coherent
> > > - * memory.
> >
> > Why do you keep deleting this statement? The driver still uses the
> > DMA-coherent memory as a workaround. Your solution doesn't solve the
> > problem completely. This is another workaround. One more time: the
> > correct solution would be to allocate a 32-bit address or some range
> > within the 4GB PCIe bus memory with no _RAM_ or some other IO behind.
> > Your solution relies on the platform firmware/glue-driver doing that,
> > which isn't universally applicable. So please don't drop the comment.
> >
> ACK.
>
> > > + * Check if the vendor driver has setup the MSI address already. If yes,
> > > + * pick up the same.
> >
> > This is inferred from the code below. So drop it.
> >
> ACK.
>
> > > This will be helpful for platforms that do not
> > > + * use/have 32-bit DMA addresses but want to use endpoints which support
> > > + * only 32-bit MSI address.
> >
> > Please merge it into the first part of the comment as like: "Permit
> > the platforms to override the MSI target address if they have a free
> > PCIe-bus memory specifically reserved for that."
> >
> ACK.
>
> > > + * Else, if the memory region is not reserved, try to allocate a 32-bit
> > > + * IOVA. Additionally, if this allocation also fails, attempt a 64-bit
> > > + * allocation. If the 64-bit MSI address is allocated, then the EPs
> > > + * supporting 32-bit MSI address will not work.
> >
> > This is easily inferred from the code below. So drop it.
> >
> ACK.
>
> > > */
> >
> > > + if (pp->msi_data)
> >
> > Note this is a physical address for which even zero value might be
> > valid. In this case it's the address of the PCIe bus space for which
> > AFAICS zero isn't reserved for something special.
> >
> That is a fair point. What do you suggest we do? Shall we define another
> op `set_msi_data` (like init/msi_init/start_link) and if it is defined
> by the vendor, then call it? Then vendor has to set the pp->msi_data
> there? Let me know.
You can define a new capability flag here
drivers/pci/controller/dwc/pcie-designware.h (see DW_PCIE_CAP_* macros)
, set it in the glue driver by means of the dw_pcie_cap_set() macro
function and instead of checking msi_data value test the flag for
being set by dw_pcie_cap_is().
>
> > > + return 0;
> > > +
> > > ret = dma_set_coherent_mask(dev, DMA_BIT_MASK(32));
> > > if (ret)
> > > dev_warn(dev, "Failed to set DMA mask to 32-bit. Devices with only 32-bit MSI support may not work properly\n");
> > > @@ -385,9 +393,15 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
> > > msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data,
> > > GFP_KERNEL);
> > > if (!msi_vaddr) {
> > > - dev_err(dev, "Failed to alloc and map MSI data\n");
> > > - dw_pcie_free_msi(pp);
> > > - return -ENOMEM;
> > > + dev_warn(dev, "Failed to alloc 32-bit MSI data. Attempting 64-bit now\n");
> > > + dma_set_coherent_mask(dev, DMA_BIT_MASK(64));
> > > + msi_vaddr = dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data,
> > > + GFP_KERNEL);
> > > + if (!msi_vaddr) {
> > > + dev_err(dev, "Failed to alloc and map MSI data\n");
> > > + dw_pcie_free_msi(pp);
> > > + return -ENOMEM;
> > > + }
> >
> > On Tue, Jan 30, 2024 at 08:40:48PM +0000, Robin Murphy wrote:
> > > Yeah, something like that. Personally I'd still be tempted to try some
> > > mildly more involved logic to just have a single dev_warn(), but I think
> > > that's less important than just having something which clearly works.
> >
> > I guess this can be done but in a bit clumsy way. Like this:
> >
> > ret = dma_set_coherent_mask(dev, DMA_BIT_MASK(32)) ||
> > !dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data, GFP_KERNEL);
> > if (ret) {
> > dev_warn(dev, "Failed to allocate 32-bit MSI target address\n");
> >
> > dma_set_coherent_mask(dev, DMA_BIT_MASK(64));
> > ret = !dmam_alloc_coherent(dev, sizeof(u64), &pp->msi_data, GFP_KERNEL);
> > if (ret) {
> > dev_err(dev, "Failed to allocate MSI target address\n");
> > return -ENOMEM;
>
> As you pointed out already, this looks pretty clumsy. I think we should
> stick to the more descriptive and readable code that I suggested.
I do not know which solution is better really. Both have pros and
cons. Let's wait for Bjorn, Mani or Robin opinion about this.
-Serge(y)
>
> > }
> > }
> >
> > Not sure whether it's much better than what Ajay suggested but at
> > least it has a single warning string describing the error, and we can
> > drop the unused msi_vaddr variable.
> >
> > -Serge(y)
> >
> > > }
> > >
> > > return 0;
> > > --
> > > 2.43.0.594.gd9cf4e227d-goog
> > >
