lkml.org 
[lkml]   [2019]   [Jun]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 1/2] dma-mapping: truncate dma masks to what dma_addr_t can hold
If I don't hear anything back in the next days I will just merge
these patches, please comment.

On Wed, May 29, 2019 at 02:22:19PM +0200, Christoph Hellwig wrote:
> Russell,
>
> any additional comments on this series?
>
> On Tue, May 21, 2019 at 03:15:03PM +0200, Christoph Hellwig wrote:
> > On Tue, May 21, 2019 at 02:04:37PM +0100, Russell King - ARM Linux admin wrote:
> > > So how does the driver negotiation for >32bit addresses work if we don't
> > > fail for large masks?
> > >
> > > I'm thinking about all those PCI drivers that need DAC cycles for >32bit
> > > addresses, such as e1000, which negotiate via (eg):
> > >
> > > /* there is a workaround being applied below that limits
> > > * 64-bit DMA addresses to 64-bit hardware. There are some
> > > * 32-bit adapters that Tx hang when given 64-bit DMA addresses
> > > */
> > > pci_using_dac = 0;
> > > if ((hw->bus_type == e1000_bus_type_pcix) &&
> > > !dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64))) {
> > > pci_using_dac = 1;
> > > } else {
> > > err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> > > if (err) {
> > > pr_err("No usable DMA config, aborting\n");
> > > goto err_dma;
> > > }
> > > }
> > >
> > > and similar. If we blindly trunate the 64-bit to 32-bit, aren't we
> > > going to end up with PCI cards using DAC cycles to a host bridge that
> > > do not support DAC cycles?
> >
> > In general PCI devices just use DAC cycles when they need it. I only
> > know of about a handful of devices that need to negotiate their
> > addressing mode, and those already use the proper API for that, which
> > is dma_get_required_mask.
> >
> > The e1000 example is a good case of how the old API confused people.
> > First it only sets the 64-bit mask for devices which can support it,
> > which is good, but then it sets the NETIF_F_HIGHDMA flag only if we
> > set a 64-bit mask, which is completely unrelated to the DMA mask,
> > it just means the driver can handle sk_buff fragments that do not
> > have a kernel mapping, which really is a driver and not a hardware
> > issue.
> >
> > So what this driver really should do is something like:
> >
> >
> > diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
> > index 551de8c2fef2..d9236083da94 100644
> > --- a/drivers/net/ethernet/intel/e1000/e1000_main.c
> > +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
> > @@ -925,7 +925,7 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
> >
> > static int cards_found;
> > static int global_quad_port_a; /* global ksp3 port a indication */
> > - int i, err, pci_using_dac;
> > + int i, err;
> > u16 eeprom_data = 0;
> > u16 tmp = 0;
> > u16 eeprom_apme_mask = E1000_EEPROM_APME;
> > @@ -996,16 +996,11 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
> > * 64-bit DMA addresses to 64-bit hardware. There are some
> > * 32-bit adapters that Tx hang when given 64-bit DMA addresses
> > */
> > - pci_using_dac = 0;
> > - if ((hw->bus_type == e1000_bus_type_pcix) &&
> > - !dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64))) {
> > - pci_using_dac = 1;
> > - } else {
> > - err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
> > - if (err) {
> > - pr_err("No usable DMA config, aborting\n");
> > - goto err_dma;
> > - }
> > + err = dma_set_mask_and_coherent(&pdev->dev,
> > + DMA_BIT_MASK(hw->bus_type == e1000_bus_type_pcix ? 64 : 32));
> > + if (err) {
> > + pr_err("No usable DMA config, aborting\n");
> > + goto err_dma;
> > }
> >
> > netdev->netdev_ops = &e1000_netdev_ops;
> > @@ -1047,19 +1042,15 @@ static int e1000_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
> >
> > netdev->priv_flags |= IFF_SUPP_NOFCS;
> >
> > - netdev->features |= netdev->hw_features;
> > + netdev->features |= netdev->hw_features | NETIF_F_HIGHDMA;
> > netdev->hw_features |= (NETIF_F_RXCSUM |
> > NETIF_F_RXALL |
> > NETIF_F_RXFCS);
> >
> > - if (pci_using_dac) {
> > - netdev->features |= NETIF_F_HIGHDMA;
> > - netdev->vlan_features |= NETIF_F_HIGHDMA;
> > - }
> > -
> > netdev->vlan_features |= (NETIF_F_TSO |
> > NETIF_F_HW_CSUM |
> > - NETIF_F_SG);
> > + NETIF_F_SG |
> > + NETIF_F_HIGHDMA);
> >
> > /* Do not set IFF_UNICAST_FLT for VMWare's 82545EM */
> > if (hw->device_id != E1000_DEV_ID_82545EM_COPPER ||
> >
> ---end quoted text---
---end quoted text---

\
 
 \ /
  Last update: 2019-06-14 09:47    [W:0.083 / U:4.296 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site