Re: [PATCH] drm/panfrost: Ignore core_mask for poweroff and sync interrupts
From: AngeloGioacchino Del Regno
Date: Thu Nov 23 2023 - 06:43:40 EST
Il 23/11/23 12:15, AngeloGioacchino Del Regno ha scritto:
Il 23/11/23 11:35, Boris Brezillon ha scritto:
On Thu, 23 Nov 2023 10:53:20 +0100
AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
wrote:
Some SoCs may be equipped with a GPU containing two core groups
and this is exactly the case of Samsung's Exynos 5422 featuring
an ARM Mali-T628 MP6 GPU: the support for this GPU in Panfrost
is partial, as this driver currently supports using only one
core group and that's reflected on all parts of it, including
the power on (and power off, previously to this patch) function.
The issue with this is that even though executing the soft reset
operation should power off all cores unconditionally, on at least
one platform we're seeing a crash that seems to be happening due
to an interrupt firing which may be because we are calling power
transition only on the first core group, leaving the second one
unchanged, or because ISR execution was pending before entering
the panfrost_gpu_power_off() function and executed after powering
off the GPU cores, or all of the above.
Finally, solve this by changing the power off flow to
1. Mask and clear all interrupts: we don't need nor want any, as
we are polling PWRTRANS anyway;
2. Call synchronize_irq() after that to make sure that any pending
ISR is executed before powering off the GPU Shaders/Tilers/L2
hence avoiding unpowered registers R/W; and
3. Ignore the core_mask and ask the GPU to poweroff both core groups
Could we split that in two patches? 1+2 in one patch, and 3 in another.
These are two orthogonal fixes IMO.
My initial idea was exactly that, but I opted for one patch doing 'em all
because a "full fix" comprises all of 1+2+3: the third one without the
first two and vice-versa may not fully resolve the issue that was seen
on the HC1 board.
So, while I agree that it'd be slightly more readable as a diff if those
were two different commits I do have reasons against splitting.....
Of course it was also necessary to add a `irq` variable to `struct
panfrost_device` as we need to get that in panfrost_gpu_power_off()
for calling synchronize_irq() on it.
Fixes: 123b431f8a5c ("drm/panfrost: Really power off GPU cores in
panfrost_gpu_power_off()")
[Regression detected on Odroid HC1, Exynos 5422, Mali-T628 MP6]
Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
---
drivers/gpu/drm/panfrost/panfrost_device.h | 1 +
drivers/gpu/drm/panfrost/panfrost_gpu.c | 26 +++++++++++++++-------
2 files changed, 19 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h
b/drivers/gpu/drm/panfrost/panfrost_device.h
index 0fc558db6bfd..b4feaa99e34f 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.h
+++ b/drivers/gpu/drm/panfrost/panfrost_device.h
@@ -94,6 +94,7 @@ struct panfrost_device {
struct device *dev;
struct drm_device *ddev;
struct platform_device *pdev;
+ int irq;
I know it's the only irq being stored at the panfrost_device level, but
I think it's clearer if we explicitly prefix it with gpu_.
Makes sense, agreed.
void __iomem *iomem;
struct clk *clock;
diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c
b/drivers/gpu/drm/panfrost/panfrost_gpu.c
index 1cc55fb9c45b..30b395125155 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
@@ -425,11 +425,21 @@ void panfrost_gpu_power_on(struct panfrost_device *pfdev)
void panfrost_gpu_power_off(struct panfrost_device *pfdev)
{
- u64 core_mask = panfrost_get_core_mask(pfdev);
int ret;
u32 val;
- gpu_write(pfdev, SHADER_PWROFF_LO, pfdev->features.shader_present &
core_mask);
+ /* We are polling PWRTRANS and we don't need nor want interrupts */
I kinda agree with that, but that's not exactly why we're
masking+syncing IRQs here. If that was the only reason, the right fix
would be to modify GPU_IRQ_MASK_ALL so it doesn't include the PWRTRANS
bits.
This fix should cover more than just the power transition IRQ use case:
we want all IRQs to be disabled before the device is suspended.
Eh I should reword that, effectively, because what I wrote as comments make
sense (as in, the logic of it completes) only if you read both of them "as one".
I'll do that in the new suspend irq helper :-)
+ gpu_write(pfdev, GPU_INT_MASK, 0);
+ gpu_write(pfdev, GPU_INT_CLEAR, GPU_IRQ_MASK_ALL);
+
+ /*
+ * Make sure that we don't have pending ISRs, otherwise we'll be
+ * reading and/or writing registers while the GPU is powered off
+ */
+ synchronize_irq(pfdev->irq);
Could we move that to a panfrost_gpu_suspend_irq() helper? I'm also not
sure making it part of panfrost_gpu_power_off() is a good idea. I'd
rather have this panfrost_gpu_suspend_irq() helper called from
panfrost_device_[runtime_]suspend(), along with
panfrost_{mmu,job}_suspend_irq().
Okay I will move that to a helper, but I still want to clarify:
- For JOB, we're checking if panfrost_job_is_idle() before trying
to runtime_suspend() (hence before trying to power off cores),
so implicitly no interrupt can fire I guess? Though there could
still be a pending ISR there too.... mmh. Brain ticking :-)
- For MMU, we're not checking anything, but I guess that if there
is no job, the mmu can't be doing anything at all?
...but then you also gave me the doubt about that one as well.
What I think that would be sensible to do is to get this commit as
a "clear" fix for the "Really power off" one, then have one or more
additional commit(s) without any fixes tag to improve the IRQ suspend
with the new mmu/job irq suspend helpers.
Of course *this* commit would introduce the panfrost_gpu_suspend_irq()
helper directly, instead of moving the logic to a helper in a later one.
Any reason against? :-)
+
+ /* Now it's safe to request poweroff for Shaders, Tilers and L2 */
It was safe before too, it's just that we probably don't want to be
In theory yes, in practice the Odroid HC1 board crashed :-P
P.S.: Joking! I understand what you're saying :-)
interrupted, if all we do is ignore the interrupts we receive, hence
the suggestion to not use GPU_IRQ_MASK_ALL, and only enable the
IRQs we care about instead.
+ gpu_write(pfdev, SHADER_PWROFF_LO, pfdev->features.shader_present);
ret = readl_relaxed_poll_timeout(pfdev->iomem + SHADER_PWRTRANS_LO,
val, !val, 1, 1000);
if (ret)
@@ -441,7 +451,7 @@ void panfrost_gpu_power_off(struct panfrost_device *pfdev)
if (ret)
dev_err(pfdev->dev, "tiler power transition timeout");
- gpu_write(pfdev, L2_PWROFF_LO, pfdev->features.l2_present & core_mask);
+ gpu_write(pfdev, L2_PWROFF_LO, pfdev->features.l2_present);
I really think we should have a helper doing the 'write(PWROFF_{LO,HI} +
poll(PWRTRANS_{LO,HI})' sequence, similar to what's done here [1][2],
such that, once we got it right for one block, we have it working for
all of them. And if there's a fix to apply, it automatically applies
to all blocks without having to fix the same bug in each copy.
...technically yes, but practically this driver doesn't currently support any
GPU that even fills the _LO registers.
I guess that we can do that later?
That's just to (paranoidly) avoid any risk to introduce other regressions in
this merge window, since we're fixing one that shouldn't have happened in the
first place...
Note that these panthor_gpu_block_power_{on,off}() helpers also handle
the case where power transitions are already in progress when you ask a
new power transition, which I don't think is checked in
panfrost_gpu_power_{off,on}().
I admit I didn't analyze the panthor driver - but here, the only power transitions
that may happen are either because of panfrost_gpu_power_on(), or because of
panfrost_gpu_power_off(), and both are polling and blocking... so from what I
understand, there's no possibility to have "another" power transition happening
while calling poweron, or poweroff.
That would change if we start to selectively turn on and off a number of shaders
and/or a number of tilers (not all of them) depending on the workload, but we're
not doing that...
...yet?
:-)
ret = readl_poll_timeout(pfdev->iomem + L2_PWRTRANS_LO,
val, !val, 0, 1000);
Not introduced by the patch, but I noticed args passed on the second
line are no longer aligned on the open parens.
Yeah, fixing that for v2 :-)
Sorry for the double reply - I just noticed that you're seeing this misalignment
because I had a *local* commit introducing that but, on linux-next, this is not
present, so there's no misalignment to fix........ :-)
Cheers,
Angelo