-----Original Message----- From: Ben Crocker [mailto:bcrocker@redhat.com] Sent: Tuesday, April 24, 2018 3:30 PM To: gregkh@linuxfoundation.org Cc: Deucher, Alexander Alexander.Deucher@amd.com; stable@vger.kernel.org Subject: Re: FAILED: patch "[PATCH] drm/radeon: insist on 32-bit DMA for Cedar on PPC64/PPC64LE" failed to apply to 4.16-stable tree

(Third try, after turning on Plain Text mode in Gmail; apologies if you got this more than once)

Hi Greg,

Thanks for the note. I think this is a case of the same change having been checked in on different branches. I downloaded the linux-4.16.3 tarball, unpacked it, and examined radeon_device.c; the correct change is there in radeon_device_init (the four lines beginning "#ifdef CONFIG_PPC64").

Looking at the whole git log, I see two instances of exactly the same patch:

commit bcb0b981c5571744ac446a6c906aa05a28d21446 Author: Ben Crocker bcrocker@redhat.com Date: Thu Feb 22 17:52:19 2018 -0500

drm/radeon: insist on 32-bit DMA for Cedar on PPC64/PPC64LE

and

commit 2c83029cda55a5e7665c7c6326909427d6a01350 Author: Ben Crocker bcrocker@redhat.com Date: Thu Feb 22 17:52:19 2018 -0500

drm/radeon: insist on 32-bit DMA for Cedar on PPC64/PPC64LE

A colleague of mine here at Red Hat thinks that no further action is necessary; please let me know what you think.

No further action is required. The patch was committed to drm-next for the next kernel and also ended up in drm-fixes for the current one at the time.

Alex

Thanks, Ben

On Sun, Apr 22, 2018 at 4:19 AM, gregkh@linuxfoundation.org wrote:

...

The patch below does not apply to the 4.16-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From bcb0b981c5571744ac446a6c906aa05a28d21446 Mon Sep 17 00:00:00

2001

...

From: Ben Crocker bcrocker@redhat.com Date: Thu, 22 Feb 2018 17:52:19 -0500 Subject: [PATCH] drm/radeon: insist on 32-bit DMA for Cedar on PPC64/PPC64LE

In radeon_device_init, set the need_dma32 flag for Cedar chips (e.g. FirePro 2270). This fixes, or at least works around, a bug on PowerPC exposed by last year's commits

8e3f1b1d8255105f31556aacf8aeb6071b00d469 (Russell Currey)

and

253fd51e2f533552ae35a0c661705da6c4842c1b (Alistair Popple)

which enabled the 64-bit DMA iommu bypass.

This caused the device to freeze, in some cases unrecoverably, and is the subject of several bug reports internal to Red Hat.

Signed-off-by: Ben Crocker bcrocker@redhat.com Signed-off-by: Alex Deucher alexander.deucher@amd.com Cc: stable@vger.kernel.org

diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c index 7f40c6f7c4dd..e415d2c097a7 100644 --- a/drivers/gpu/drm/radeon/radeon_device.c +++ b/drivers/gpu/drm/radeon/radeon_device.c @@ -1366,6 +1366,10 @@ int radeon_device_init(struct radeon_device

*rdev,

...

    if ((rdev->flags & RADEON_IS_PCI) &&
        (rdev->family <= CHIP_RS740))
            rdev->need_dma32 = true;

+#ifdef CONFIG_PPC64

•   if (rdev->family == CHIP_CEDAR)
  

•           rdev->need_dma32 = true; #endif
  
    dma_bits = rdev->need_dma32 ? 32 : 40;
    r = pci_set_dma_mask(rdev->pdev, DMA_BIT_MASK(dma_bits));