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

[Frank Li <Frank.li@nxp.com>]

On Thu, Aug 08, 2024 at 12:35:01AM +0200, Niklas Cassel wrote:
> 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).

Yes, 32bit is limited by internal bus farbic, not AHCI controller.

It look like
hsio-bus
{
	dma-ranges = <low 4G space>
	sata@addr
	{
		...
	}
}

This should be correct reflect hardware behavior.  force ahci to 32bit dma
mask should be a wordaround.

Frank

>
> 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