The full text of the preceding comment explains the need:
/*
* The atl1c chip can DMA to 64-bit addresses, but it uses a single
* shared register for the high 32 bits, so only a single, aligned,
* 4 GB physical address range can be used at a time.
*
* Supporting 64-bit DMA on this hardware is more trouble than it's
* worth. It is far easier to limit to 32-bit DMA than update
* various kernel subsystems to support the mechanics required by a
* fixed-high-32-bit system.
*/
Without this, we get data corruption and crashes on machines with 4 GB
of RAM or more.
- Chris
On Mon, Nov 16, 2020 at 11:14 PM Heiner Kallweit <hkallwe...@gmail.com> wrote:
>
> Am 17.11.2020 um 03:55 schrieb Zhang Changzhong:
> > Fix to return a negative error code from the error handling
> > case instead of 0, as done elsewhere in this function.
> >
> > Fixes: 85eb5bc33717 ("net: atheros: switch from 'pci_' to 'dma_' API")
> > Reported-by: Hulk Robot <hul...@huawei.com>
> > Signed-off-by: Zhang Changzhong <zhangchangzh...@huawei.com>
> > ---
> > drivers/net/ethernet/atheros/atl1c/atl1c_main.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> > b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> > index 0c12cf7..3f65f2b 100644
> > --- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> > +++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> > @@ -2543,8 +2543,8 @@ static int atl1c_probe(struct pci_dev *pdev, const
> > struct pci_device_id *ent)
> > * various kernel subsystems to support the mechanics required by a
> > * fixed-high-32-bit system.
> > */
> > - if ((dma_set_mask(&pdev->dev, DMA_BIT_MASK(32)) != 0) ||
> > - (dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32)) != 0)) {
> > + err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
>
> I wonder whether you need this call at all, because 32bit is the default.
> See following
>
> "By default, the kernel assumes that your device can address 32-bits
> of DMA addressing."
>
> in https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt
>
> > + if (err) {
> > dev_err(&pdev->dev, "No usable DMA configuration,aborting\n");
> > goto err_dma;
> > }
> >
>
