From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Brugger Subject: Re: [PATCH v8 2/3] CMDQ: Mediatek CMDQ driver Date: Tue, 21 Jun 2016 15:41:33 +0200 Message-ID: <5769440D.5030505@gmail.com> References: <1464578397-29743-1-git-send-email-hs.liao@mediatek.com> <1464578397-29743-3-git-send-email-hs.liao@mediatek.com> <574C5CBF.7060002@gmail.com> <1464683762.14604.59.camel@mtksdaap41> <574DEE40.9010008@gmail.com> <1464775020.11122.40.camel@mtksdaap41> <574FF264.7050209@gmail.com> <1464934356.15175.31.camel@mtksdaap41> <57516774.5080008@gmail.com> <1464956037.16029.8.camel@mtksdaap41> <575181E5.6090603@gmail.com> <5756FD73.3050607@gmail.com> <1465364427.9963.13.camel@mtksdaap41> <5757F762.4020908@gmail.com> <1465388727.21326.8.camel@mtksdaap41> <57583B45.2080504@gmail.com> <1465890268.7191.13.camel@mtksdaap41> <575FD9BA.8040708@gmail.com> <1465906063.20796.20.camel@mtksdaap41> <1466152107.11184.14.camel@mtksdaap41> <57641E01.3070205@gmail.com> <1466488358.8045.19.camel@mtksdaap41> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1466488358.8045.19.camel@mtksdaap41> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+glpam-linux-mediatek=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org To: Horng-Shyang Liao Cc: Monica Wang , Jiaguang Zhang , Nicolas Boichat , jassisinghbrar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, cawa cheng , Bibby Hsieh , YT Shen , Damon Chu , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Sascha Hauer , Daoyuan Huang , Sascha Hauer , Glory Hung , CK HU , Rob Herring , linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, srv_heupstream-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org, jaswinder.singh-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, Josh-YC Liu , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Dennis-YC Hsieh , Philipp Zabel List-Id: devicetree@vger.kernel.org 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 > > 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 > >