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annotate sources/patches/linux-arm-qemuirq.patch @ 1781:b27851ab2795 draft

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Vo Minh Thu was surprised by toybox replacing busybox and requested I update about.html.
author Rob Landley <rob@landley.net>
date Tue, 04 Aug 2015 14:40:20 -0500
parents 1b2017d3ecf5
children
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1b2017d3ecf5 Undo random arm IRQ routing breakage du jour, yet again.
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1 Modify arm IRQ setup to work with all versions of qemu since 1.0.
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2
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3 For many years, the kernel's versatile board setup expected all devices
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4 to share IRQ 27, and QEMU 1.2 helpfully emulated hardware that did that
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5 (or used IRQ 59 if the IRQ controller was told to shift everything up 32
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6 places). This wasn't what the actual hardware did, but nobody noticed for
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7 over a decade because this reference board was long-gone and only useful
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8 as a base for virtualization.
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9
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10 Then the kernel developers noticed that the default IRQ range could
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11 (theoretically) use IRQ 0 as an actual IRQ, so they poked the "move everything
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12 up 32 places" register... and got the math wrong calculating the new IRQ
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13 to expect stuff on. (Because just adding 32 wouldn't be the right thing to
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14 do, you've gotta do a multi-stage process going through three different
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15 functions with a callback.)
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16
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17 When informed they'd broken qemu, they looked up old Versatile documentation
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18 and realized what they'd done had never matched real hardware, and adjusted
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19 it to some other random value: still getting the math wrong. Then they finally
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20 fixed the wrong math, but it turns out the documentation they were using
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21 didn't match what actual hardware was doing, or something. All in all they
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22 changed the IRQ mapping at least _4_TIMES_ before finally unearthing an
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23 actual Versatile board out of some landfill or other to test it out on.
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24 Needless to say, "this breaks QEMU" was not considered a valid data point.
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25
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26 Meanwhile, QEMU 1.2 and earlier only supported the "everything on irq 27" mode,
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27 and the next several releases supported random potluck things the kernel du
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28 jour did, but current ones don't.
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29
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30 BUT: if you the kernel requests irq 27 from the controller as
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31 its first action, QEMU thinks you're running an old "everying on 27" kernel
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32 and triggers an emulation mode that puts everything on IRQ 27 (or 59 if
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33 you flip the add 32 bit in the controller, meaning current kernels aren't
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34 bothered by IRQ 0 being potentially used). And this runs on all the qemu
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35 versions since 1.0. (Although you still don't want to use QEMU 1.3 and 1.4
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36 because they had a bug in TCG that got the size of translated blocks wrong
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37 causing spurious but highly intermittent segfaults...)
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38
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39 Note, I broke this patch out of the big arm patch after the FIFTH time
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40 they made changes that prevented this patch from cleanly applying.
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41
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42 diff --git a/arch/arm/mach-versatile/pci.c b/arch/arm/mach-versatile/pci.c
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43 index c97be4e..da0342d 100644
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44 --- a/arch/arm/mach-versatile/pci.c
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45 +++ b/arch/arm/mach-versatile/pci.c
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46 @@ -305,7 +305,7 @@ int __init pci_versatile_setup(int nr, struct pci_sys_data *sys)
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47 * real hardware behaviour and it need not be backwards
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48 * compatible for us. This write is harmless on real hardware.
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49 */
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50 - __raw_writel(0, VERSATILE_PCI_VIRT_BASE+PCI_INTERRUPT_LINE);
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51 + __raw_writel(27, VERSATILE_PCI_VIRT_BASE+PCI_INTERRUPT_LINE);
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52
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53 /*
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54 * Do not to map Versatile FPGA PCI device into memory space
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55 @@ -346,7 +346,7 @@ static int __init versatile_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
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56 * 30 PCI0 PCI1 PCI2 PCI3
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57 * 29 PCI3 PCI0 PCI1 PCI2
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58 */
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59 - irq = IRQ_SIC_PCI0 + ((slot + 2 + pin - 1) & 3);
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60 + irq = 59;
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61
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62 return irq;
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63 }