Re: [PATCH v8 2/3] CMDQ: Mediatek CMDQ driver

Horng-Shyang Liao
2016-06-22T05:43:13Z

On Tue, 2016-06-21 at 15:41 +0200, Matthias Brugger wrote:
>
> On 21/06/16 07:52, Horng-Shyang Liao wrote:
> > On Fri, 2016-06-17 at 17:57 +0200, Matthias Brugger wrote:
> >>
> >> On 17/06/16 10:28, Horng-Shyang Liao wrote:
> >>> Hi Matthias,
> >>>
> >>> On Tue, 2016-06-14 at 20:07 +0800, Horng-Shyang Liao wrote:
> >>>> Hi Matthias,
> >>>>
> >>>> On Tue, 2016-06-14 at 12:17 +0200, Matthias Brugger wrote:
> >>>>>
> >>>>> On 14/06/16 09:44, Horng-Shyang Liao wrote:
> >>>>>> Hi Matthias,
> >>>>>>
> >>>>>> On Wed, 2016-06-08 at 17:35 +0200, Matthias Brugger wrote:
> >>>>>>>
> >>>>>>> On 08/06/16 14:25, Horng-Shyang Liao wrote:
> >>>>>>>> Hi Matthias,
> >>>>>>>>
> >>>>>>>> On Wed, 2016-06-08 at 12:45 +0200, Matthias Brugger wrote:
> >>>>>>>>>
> >>>>>>>>> On 08/06/16 07:40, Horng-Shyang Liao wrote:
> >>>>>>>>>> Hi Matthias,
> >>>>>>>>>>
> >>>>>>>>>> On Tue, 2016-06-07 at 18:59 +0200, Matthias Brugger wrote:
> >>>>>>>>>>>
> >>>>>>>>>>> On 03/06/16 15:11, Matthias Brugger wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>> [...]
> >>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>> + smp_mb(); /* modify jump before enable thread */
> >>>>>>>>>>>>>>>>>>>>> + }
> >>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>> + cmdq_thread_writel(thread, task->pa_base +
> >>>>>>>>>>>>>>>>>>>>> task->command_size,
> >>>>>>>>>>>>>>>>>>>>> + CMDQ_THR_END_ADDR);
> >>>>>>>>>>>>>>>>>>>>> + cmdq_thread_resume(thread);
> >>>>>>>>>>>>>>>>>>>>> + }
> >>>>>>>>>>>>>>>>>>>>> + list_move_tail(&task->list_entry, &thread->task_busy_list);
> >>>>>>>>>>>>>>>>>>>>> + spin_unlock_irqrestore(&cmdq->exec_lock, flags);
> >>>>>>>>>>>>>>>>>>>>> +}
> >>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>> +static void cmdq_handle_error_done(struct cmdq *cmdq,
> >>>>>>>>>>>>>>>>>>>>> + struct cmdq_thread *thread, u32 irq_flag)
> >>>>>>>>>>>>>>>>>>>>> +{
> >>>>>>>>>>>>>>>>>>>>> + struct cmdq_task *task, *tmp, *curr_task = NULL;
> >>>>>>>>>>>>>>>>>>>>> + u32 curr_pa;
> >>>>>>>>>>>>>>>>>>>>> + struct cmdq_cb_data cmdq_cb_data;
> >>>>>>>>>>>>>>>>>>>>> + bool err;
> >>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>> + if (irq_flag & CMDQ_THR_IRQ_ERROR)
> >>>>>>>>>>>>>>>>>>>>> + err = true;
> >>>>>>>>>>>>>>>>>>>>> + else if (irq_flag & CMDQ_THR_IRQ_DONE)
> >>>>>>>>>>>>>>>>>>>>> + err = false;
> >>>>>>>>>>>>>>>>>>>>> + else
> >>>>>>>>>>>>>>>>>>>>> + return;
> >>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>> + curr_pa = cmdq_thread_readl(thread, CMDQ_THR_CURR_ADDR);
> >>>>>>>>>>>>>>>>>>>>> +
> >>>>>>>>>>>>>>>>>>>>> + list_for_each_entry_safe(task, tmp, &thread->task_busy_list,
> >>>>>>>>>>>>>>>>>>>>> + list_entry) {
> >>>>>>>>>>>>>>>>>>>>> + if (curr_pa >= task->pa_base &&
> >>>>>>>>>>>>>>>>>>>>> + curr_pa < (task->pa_base + task->command_size))
> >>>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>>> What are you checking here? It seems as if you make some implcit
> >>>>>>>>>>>>>>>>>>>> assumptions about pa_base and the order of execution of
> >>>>>>>>>>>>>>>>>>>> commands in the
> >>>>>>>>>>>>>>>>>>>> thread. Is it save to do so? Does dma_alloc_coherent give any
> >>>>>>>>>>>>>>>>>>>> guarantees
> >>>>>>>>>>>>>>>>>>>> about dma_handle?
> >>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>> 1. Check what is the current running task in this GCE thread.
> >>>>>>>>>>>>>>>>>>> 2. Yes.
> >>>>>>>>>>>>>>>>>>> 3. Yes, CMDQ doesn't use iommu, so physical address is continuous.
> >>>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> Yes, physical addresses might be continous, but AFAIK there is no
> >>>>>>>>>>>>>>>>>> guarantee that the dma_handle address is steadily growing, when
> >>>>>>>>>>>>>>>>>> calling
> >>>>>>>>>>>>>>>>>> dma_alloc_coherent. And if I understand the code correctly, you
> >>>>>>>>>>>>>>>>>> use this
> >>>>>>>>>>>>>>>>>> assumption to decide if the task picked from task_busy_list is
> >>>>>>>>>>>>>>>>>> currently
> >>>>>>>>>>>>>>>>>> executing. So I think this mecanism is not working.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>> I don't use dma_handle address, and just use physical addresses.
> >>>>>>>>>>>>>>>>> From CPU's point of view, tasks are linked by the busy list.
> >>>>>>>>>>>>>>>>> From GCE's point of view, tasks are linked by the JUMP command.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>>> In which cases does the HW thread raise an interrupt.
> >>>>>>>>>>>>>>>>>> In case of error. When does CMDQ_THR_IRQ_DONE get raised?
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>> GCE will raise interrupt if any task is done or error.
> >>>>>>>>>>>>>>>>> However, GCE is fast, so CPU may get multiple done tasks
> >>>>>>>>>>>>>>>>> when it is running ISR.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>> In case of error, that GCE thread will pause and raise interrupt.
> >>>>>>>>>>>>>>>>> So, CPU may get multiple done tasks and one error task.
> >>>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> I think we should reimplement the ISR mechanism. Can't we just read
> >>>>>>>>>>>>>>>> CURR_IRQ_STATUS and THR_IRQ_STATUS in the handler and leave
> >>>>>>>>>>>>>>>> cmdq_handle_error_done to the thread_fn? You will need to pass
> >>>>>>>>>>>>>>>> information from the handler to thread_fn, but that shouldn't be an
> >>>>>>>>>>>>>>>> issue. AFAIK interrupts are disabled in the handler, so we should stay
> >>>>>>>>>>>>>>>> there as short as possible. Traversing task_busy_list is expensive, so
> >>>>>>>>>>>>>>>> we need to do it in a thread context.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> Actually, our initial implementation is similar to your suggestion,
> >>>>>>>>>>>>>>> but display needs CMDQ to return callback function very precisely,
> >>>>>>>>>>>>>>> else display will drop frame.
> >>>>>>>>>>>>>>> For display, CMDQ interrupt will be raised every 16 ~ 17 ms,
> >>>>>>>>>>>>>>> and CMDQ needs to call callback function in ISR.
> >>>>>>>>>>>>>>> If we defer callback to workqueue, the time interval may be larger than
> >>>>>>>>>>>>>>> 32 ms.sometimes.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> I think the problem is, that you implemented the workqueue as a ordered
> >>>>>>>>>>>>>> workqueue, so there is no parallel processing. I'm still not sure why
> >>>>>>>>>>>>>> you need the workqueue to be ordered. Can you please explain.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> The order should be kept.
> >>>>>>>>>>>>> Let me use mouse cursor as an example.
> >>>>>>>>>>>>> If task 1 means move mouse cursor to point A, task 2 means point B,
> >>>>>>>>>>>>> and task 3 means point C, our expected result is A -> B -> C.
> >>>>>>>>>>>>> If the order is not kept, the result could become A -> C -> B.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>> Got it, thanks for the clarification.
> >>>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> I think a way to get rid of the workqueue is to use a timer, which gets
> >>>>>>>>>>> programmed to the time a timeout in the first task in the busy list
> >>>>>>>>>>> would happen. Everytime we update the busy list (e.g. because of task
> >>>>>>>>>>> got finished by the thread), we update the timer. When the timer
> >>>>>>>>>>> triggers, which hopefully won't happen too often, we return timeout on
> >>>>>>>>>>> the busy list elements, until the time is lower then the actual time.
> >>>>>>>>>>>
> >>>>>>>>>>> At least with this we can reduce the data structures in this driver and
> >>>>>>>>>>> make it more lightweight.
> >>>>>>>>>>
> >>>>>>>>>> From my understanding, your proposed method can handle timeout case.
> >>>>>>>>>>
> >>>>>>>>>> However, the workqueue is also in charge of releasing tasks.
> >>>>>>>>>> Do you take releasing tasks into consideration by using the proposed
> >>>>>>>>>> timer method?
> >>>>>>>>>> Furthermore, I think the code will become more complex if we also use
> >>>>>>>>>> timer to implement releasing tasks.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Can't we call
> >>>>>>>>> clk_disable_unprepare(cmdq->clock);
> >>>>>>>>> cmdq_task_release(task);
> >>>>>>>>> after invoking the callback?
> >>>
> >>> After I put clk_disable_unprepare(cmdq->clock) into ISR, I encounter
> >>> another BUG.
> >>>
> >>> (Quote some Linux 4.7 source code.)
> >>>
> >>> 605 void clk_unprepare(struct clk *clk)
> >>> 606 {
> >>> 607 if (IS_ERR_OR_NULL(clk))
> >>> 608 return;
> >>> 609
> >>> 610 clk_prepare_lock(); // <-- Here
> >>> 611 clk_core_unprepare(clk->core);
> >>> 612 clk_prepare_unlock();
> >>> 613 }
> >>> 614 EXPORT_SYMBOL_GPL(clk_unprepare);
> >>>
> >>> 91 static void clk_prepare_lock(void)
> >>> 92 {
> >>> 93 if (!mutex_trylock(&prepare_lock)) { // <-- Here
> >>> 94 if (prepare_owner == current) {
> >>> 95 prepare_refcnt++;
> >>> 96 return;
> >>> 97 }
> >>> 98 mutex_lock(&prepare_lock);
> >>> 99 }
> >>> 100 WARN_ON_ONCE(prepare_owner != NULL);
> >>> 101 WARN_ON_ONCE(prepare_refcnt != 0);
> >>> 102 prepare_owner = current;
> >>> 103 prepare_refcnt = 1;
> >>> 104 }
> >>>
> >>> So, 'unprepare' can sleep and cannot be put into ISR.
> >>> I also try to put it into a timer, but the error is the same
> >>> since timer callback is executed by softirq.
> >>>
> >>> We need clk_disable_unprepare() since it can save power consumption
> >>> in idle.
> >>
> >> We can call clk_prepare in probe and then use clk_enable/clk_disable,
> >> which don't sleep.
> >>
> >> Regards,
> >> Matthias
> >
> > Hi Matthias,
> >
> > Because clock gate and MUX are controlled by clk_enable/clk_disable,
> > and PLL is controlled by clk_prepare/clk_unprepare,
> > I still need to call clk_unprepare.
> >
> > After I remove releasing buffer, releasing task, and timeout task from
> > work, the work can be detached from task.
> >
> > Therefore, I can use the following flow to reduce the number of works.
> >
> > if task_busy_list from empty to non-empty
> > clk_prepare_enable
> > if task_busy_list from non-empty to empty
> > in ISR, add work for clk_disable_unprepare
> >
> > What do you think of this solution?
>
> Can't we just call clk_prepare in probe and clk_unprepare in remove? I
> think this could be a good starting point, and if we see, that we need
> to save more energy in the future, we can think of some other mechanism.
> What do you think?
>
> Regards,
> Matthias

Hi Matthias,

As far as I know, we should call clk_unprepare to save more energy.

May I call clk_prepare in probe/resume and clk_unprepare in
remove/suspend in this patch, and then prepare another patch to call
clk_unprepare in idle to save more energy?

Thanks,
HS

> >
> > Thanks,
> > HS
> >
> >>> Therefore, I plan to
> >>> (1) move releasing buffer and task into ISR,
> >>> (2) move timeout into timer, and
> >>> (3) keep workqueue for clk_disable_unprepare().
> >>>
> >>> What do you think?
> >>>
> >>> Thanks,
> >>> HS
> >>>
> >>>>>>>>
> >>>>>>>> Do you mean just call these two functions in ISR?
> >>>>>>>> My major concern is dma_free_coherent() and kfree() in
> >>>>>>>> cmdq_task_release(task).
> >>>>>>>
> >>>>>>> Why do we need the dma calls at all? Can't we just calculate the
> >>>>>>> physical address using __pa(x)?
> >>>>>>
> >>>>>> I prefer to use dma_map_single/dma_unmap_single.
> >>>>>>
> >>>>>
> >>>>> Can you please elaborate why you need this. We don't do dma, so we
> >>>>> should not use dma memory for this.
> >>>>
> >>>> We need a buffer to share between CPU and GCE, so we do need DMA.
> >>>> CPU is in charge of writing GCE commands into this buffer.
> >>>> GCE is in charge of reading and running GCE commands from this buffer.
> >>>> When we chain CMDQ tasks, we also need to modify GCE JUMP command.
> >>>> Therefore, I prefer to use dma_alloc_coherent and dma_free_coherent.
> >>>>
> >>>> However, if we want to use timer to handle timeout, we need to release
> >>>> memory in ISR.
> >>>> In this case, using kmalloc/kfree + dma_map_single/dma_unmap_single
> >>>> instead of dma_alloc_coherent/dma_free_coherent is an alternative
> >>>> solution, but taking care the synchronization between cache and memory
> >>>> is the expected overhead.
> >>>>
> >>>>>>>> Therefore, your suggestion is to use GFP_ATOMIC for both
> >>>>>>>> dma_alloc_coherent() and kzalloc(). Right?
> >>>>>>>
> >>>>>>> I don't think we need GFP_ATOMIC, the critical path will just free the
> >>>>>>> memory.
> >>>>>>
> >>>>>> I tested these two functions, and kfree was safe.
> >>>>>> However, dma_free_coherent raised BUG.
> >>>>>> BUG: failure at
> >>>>>> /mnt/host/source/src/third_party/kernel/v3.18/mm/vmalloc.c:1514/vunmap()!
> >>>>>
> >>>>> Just a general hint. Please try to evaluate on a recent kernel. It looks
> >>>>> like as if you tried this on a v3.18 based one.
> >>>>
> >>>> This driver should be backward compatible to v3.18 for a MTK project.
> >>>>
> >>>>> Best regards,
> >>>>> Matthias
> >>>>
> >>>> Thanks,
> >>>> HS
> >>>>
> >>>>>> 1512 void vunmap(const void *addr)
> >>>>>> 1513 {
> >>>>>> 1514 BUG_ON(in_interrupt()); // <-- here
> >>>>>> 1515 might_sleep();
> >>>>>> 1516 if (addr)
> >>>>>> 1517 __vunmap(addr, 0);
> >>>>>> 1518 }
> >>>>>> 1519 EXPORT_SYMBOL(vunmap);
> >>>>>>
> >>>>>> Therefore, I plan to use kmalloc + dma_map_single instead of
> >>>>>> dma_alloc_coherent, and dma_unmap_single + kfree instead of
> >>>>>> dma_free_coherent.
> >>>>>>
> >>>>>> What do you think about the function replacement?
> >>>>>>
> >>>>>>>> If so, I can try to implement timeout by timer, and discuss with you
> >>>>>>>> if I have further questions.
> >>>>>>>>
> >>>>>>>
> >>>>>>> Sounds good :)
> >>>>>>>
> >>>>>>> Thanks,
> >>>>>>> Matthias
> >>>>>>
> >>>>>> Thanks,
> >>>>>> HS
> >>>>>>
> >>>>>>>>> Regrading the clock, wouldn't it be easier to handle the clock
> >>>>>>>>> enable/disable depending on the state of task_busy_list? I suppose we
> >>>>>>>>> can't as we would need to check the task_busy_list of all threads, right?
> >>>>>>>>>
> >>>>>>>>> Regards,
> >>>>>>>>> Matthias
> >>>>>>>>
> >>>>>>>> Thanks,
> >>>>>>>> HS
> >
> >