On Thu, Sep 21, 2023 at 07:59:51PM +0200, Christophe JAILLET wrote:
> Le 21/09/2023 à 17:37, Frank Li a écrit :
> > From: Guanhua Gao <guanhua.gao@xxxxxxx>
> >
> > Set DMA mask and coherent DMA mask to enable 64-bit addressing.
> >
> > Signed-off-by: Guanhua Gao <guanhua.gao@xxxxxxx>
> > Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@xxxxxxx>
> > Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
> > ---
> > drivers/pci/controller/dwc/pci-layerscape-ep.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-layerscape-ep.c b/drivers/pci/controller/dwc/pci-layerscape-ep.c
> > index de4c1758a6c33..6fd0dea38a32c 100644
> > --- a/drivers/pci/controller/dwc/pci-layerscape-ep.c
> > +++ b/drivers/pci/controller/dwc/pci-layerscape-ep.c
> > @@ -249,6 +249,11 @@ static int __init ls_pcie_ep_probe(struct platform_device *pdev)
> > pcie->big_endian = of_property_read_bool(dev->of_node, "big-endian");
> > + /* set 64-bit DMA mask and coherent DMA mask */
> > + if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64)))
> > + if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32)))
>
> As stated in [1], dma_set_mask() with a 64-bit mask will never
> fail if dev->dma_mask is non-NULL.
>
> So, if it fails, the 32 bits case will also fail for the same reason.
> There is no need for the 2nd test.
>
>
> See [1] for Christoph Hellwig comment about it.
I don't think it is true. the below is dma_set_mask()'s implementation
int dma_set_mask(struct device *dev, u64 mask)
{
/*
* Truncate the mask to the actually supported dma_addr_t width to
* avoid generating unsupportable addresses.
*/
mask = (dma_addr_t)mask;
if (!dev->dma_mask || !dma_supported(dev, mask))
^^^^^^^
return -EIO;
arch_dma_set_mask(dev, mask);
*dev->dma_mask = mask;
return 0;
}
dma_supported() may return failiure.
static int dma_supported(struct device *dev, u64 mask)
{
const struct dma_map_ops *ops = get_dma_ops(dev);
/*
* ->dma_supported sets the bypass flag, so we must always call
* into the method here unless the device is truly direct mapped.
*/
if (!ops)
return dma_direct_supported(dev, mask);
if (!ops->dma_supported)
return 1;
return ops->dma_supported(dev, mask);
^^^^^^
DMA driver or IOMMU driver may return failure.
}
Frank
>
> CJ
>
>
> [1]: https://lkml.org/lkml/2021/6/7/398
>
> > + return -EIO;
> > +
> > platform_set_drvdata(pdev, pcie);
> > ret = dw_pcie_ep_init(&pci->ep);
>
