lkml.org 
[lkml]   [2015]   [Apr]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH v4 1/4] PCI: X-Gene: Add the APM X-Gene v1 PCIe MSI/MSIX termination driver
Date
On Sunday 19 April 2015 11:40:09 Duc Dang wrote:
> On Fri, Apr 17, 2015 at 7:10 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Friday 17 April 2015 02:50:07 Duc Dang wrote:
> >> +
> >> + /*
> >> + * MSIINTn (n is 0..F) indicates if there is a pending MSI interrupt
> >> + * If bit x of this register is set (x is 0..7), one or more interupts
> >> + * corresponding to MSInIRx is set.
> >> + */
> >> + grp_select = readl(xgene_msi->msi_regs + MSI_INT0 + (msi_grp << 16));
> >> + while (grp_select) {
> >> + msir_index = ffs(grp_select) - 1;
> >> + /*
> >> + * Calculate MSInIRx address to read to check for interrupts
> >> + * (refer to termination address and data assignment
> >> + * described in xgene_compose_msi_msg function)
> >> + */
> >> + msir_reg = (msi_grp << 19) + (msir_index << 16);
> >> + msir_val = readl(xgene_msi->msi_regs + MSI_IR0 + msir_reg);
> >> + while (msir_val) {
> >> + intr_index = ffs(msir_val) - 1;
> >> + /*
> >> + * Calculate MSI vector number (refer to the termination
> >> + * address and data assignment described in
> >> + * xgene_compose_msi_msg function)
> >> + */
> >> + hw_irq = (((msir_index * IRQS_PER_IDX) + intr_index) *
> >> + NR_HW_IRQS) + msi_grp;
> >> + virq = irq_find_mapping(xgene_msi->domain, hw_irq);
> >> + if (virq != 0)
> >> + generic_handle_irq(virq);
> >> + msir_val &= ~(1 << intr_index);
> >> + processed++;
> >> + }
> >> + grp_select &= ~(1 << msir_index);
> >> + }
> >>
> >
> > As the MSI is forwarded to the GIC here, how do you maintain ordering
> > between DMA data getting forwarded from the PCI host bridge to RAM
> > with regard to the MSI handler getting entered from this code?
>
> When device perform a DMA transfer, the order of PCIE inbound requests
> will be like this:
> 1. DMA data get transferred via PCIe inbound request
> 2. After devices issue DMA transfer request, the device fires an MSI
> interrupt by issuing another inbound write to write MSI data to MSI
> termination address.
>
> As these 2 requests are transferred via PCIe bus in order, the DMA
> data will be all in DDR before the MSI data hit the termination
> address to trigger the MSI handler in interrupt handler code.

Obviously they appear on the PCI host bridge in order, because that
is a how PCI works. My question was about what happens then. On a lot
of SoCs, there is something like an AXI bus that uses posted
transactions between PCI and RAM, so you have a do a full manual
syncronization of ongoing PIC DMAs when the MSI catcher signals the
top-level interrupt. Do you have a bus between PCI and RAM that does
not require this, or does the MSI catcher have logic to flush all DMAs?

Arnd


\
 
 \ /
  Last update: 2015-04-19 22:21    [W:0.134 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site