Re: [PATCH v4 4/6] ata: ahci_imx: Add 32bits DMA limit for i.MX8QM AHCI SATA

[Niklas Cassel <cassel@kernel.org>]

On Fri, Aug 02, 2024 at 02:30:45AM +0000, Hongxing Zhu wrote:
> >
> > Does this solve your problem:
> > diff --git a/drivers/ata/libahci_platform.c b/drivers/ata/libahci_platform.c
> > index 581704e61f28..fc86e2c8c42b 100644
> > --- a/drivers/ata/libahci_platform.c
> > +++ b/drivers/ata/libahci_platform.c
> > @@ -747,12 +747,11 @@ int ahci_platform_init_host(struct platform_device
> > *pdev,
> >                         ap->ops = &ata_dummy_port_ops;
> >         }
> >
> > -       if (hpriv->cap & HOST_CAP_64) {
> > -               rc = dma_coerce_mask_and_coherent(dev,
> > DMA_BIT_MASK(64));
> > -               if (rc) {
> > -                       dev_err(dev, "Failed to enable 64-bit DMA.\n");
> > -                       return rc;
> > -               }
> > +       rc = dma_coerce_mask_and_coherent(dev,
> > +                       DMA_BIT_MASK((hpriv->cap & HOST_CAP_64) ? 64 :
> > 32));
> > +       if (rc) {
> > +               dev_err(dev, "DMA enable failed\n");
> > +               return rc;
> >         }
> >
> >         rc = ahci_reset_controller(host);
> >
> Hi Niklas:
> I'm so sorry to reply late.
> About the 32bit DMA limitation of i.MX8QM AHCI SATA.
> It's seems that one "dma-ranges" property in the DT can let i.MX8QM SATA
>  works fine in my past days tests without this commit.
> How about drop these driver changes, and add "dma-ranges" for i.MX8QM SATA?
> Thanks a lot for your kindly help.

Hello Richard,

did you try my suggested patch above?


If you look at dma-ranges:
https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#dma-ranges

"dma-ranges" property should be used on a bus device node
(such as PCI host bridges).

It does not seem correct to add this property (describing the DMA limit
of the AHCI controller, a PCI endpoint) on the PCI host bridge/controller.

This property belongs to the AHCI controller, not the upstream PCI
host bridge/controller.

AHCI has a specific register to describe if the hardware can support
64-bit DMA addresses or not, so if my suggested patch works for you,
it seems like a more elegant solution (which also avoids having to
abuse device tree properties).


Kind regards,
Niklas