[PATCH v4 1/1] dmaengine: owl: Use correct lock in owl_dma_get_pchan()

[Cristian Ciocaltea]

When the kernel is built with lockdep support and the owl-dma driver is
used, the following message is shown:

[    2.496939] INFO: trying to register non-static key.
[    2.501889] the code is fine but needs lockdep annotation.
[    2.507357] turning off the locking correctness validator.
[    2.512834] CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.6.3+ #15
[    2.519084] Hardware name: Generic DT based system
[    2.523878] Workqueue: events_freezable mmc_rescan
[    2.528681] [<801127f0>] (unwind_backtrace) from [<8010da58>] (show_stack+0x10/0x14)
[    2.536420] [<8010da58>] (show_stack) from [<8080fbe8>] (dump_stack+0xb4/0xe0)
[    2.543645] [<8080fbe8>] (dump_stack) from [<8017efa4>] (register_lock_class+0x6f0/0x718)
[    2.551816] [<8017efa4>] (register_lock_class) from [<8017b7d0>] (__lock_acquire+0x78/0x25f0)
[    2.560330] [<8017b7d0>] (__lock_acquire) from [<8017e5e4>] (lock_acquire+0xd8/0x1f4)
[    2.568159] [<8017e5e4>] (lock_acquire) from [<80831fb0>] (_raw_spin_lock_irqsave+0x3c/0x50)
[    2.576589] [<80831fb0>] (_raw_spin_lock_irqsave) from [<8051b5fc>] (owl_dma_issue_pending+0xbc/0x120)
[    2.585884] [<8051b5fc>] (owl_dma_issue_pending) from [<80668cbc>] (owl_mmc_request+0x1b0/0x390)
[    2.594655] [<80668cbc>] (owl_mmc_request) from [<80650ce0>] (mmc_start_request+0x94/0xbc)
[    2.602906] [<80650ce0>] (mmc_start_request) from [<80650ec0>] (mmc_wait_for_req+0x64/0xd0)
[    2.611245] [<80650ec0>] (mmc_wait_for_req) from [<8065aa10>] (mmc_app_send_scr+0x10c/0x144)
[    2.619669] [<8065aa10>] (mmc_app_send_scr) from [<80659b3c>] (mmc_sd_setup_card+0x4c/0x318)
[    2.628092] [<80659b3c>] (mmc_sd_setup_card) from [<80659f0c>] (mmc_sd_init_card+0x104/0x430)
[    2.636601] [<80659f0c>] (mmc_sd_init_card) from [<8065a3e0>] (mmc_attach_sd+0xcc/0x16c)
[    2.644678] [<8065a3e0>] (mmc_attach_sd) from [<8065301c>] (mmc_rescan+0x3ac/0x40c)
[    2.652332] [<8065301c>] (mmc_rescan) from [<80143244>] (process_one_work+0x2d8/0x780)
[    2.660239] [<80143244>] (process_one_work) from [<80143730>] (worker_thread+0x44/0x598)
[    2.668323] [<80143730>] (worker_thread) from [<8014b5f8>] (kthread+0x148/0x150)
[    2.675708] [<8014b5f8>] (kthread) from [<801010b4>] (ret_from_fork+0x14/0x20)
[    2.682912] Exception stack(0xee8fdfb0 to 0xee8fdff8)
[    2.687954] dfa0:                                     00000000 00000000 00000000 00000000
[    2.696118] dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    2.704277] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000

The obvious fix would be to use 'spin_lock_init()' on 'pchan->lock'
before attempting to call 'spin_lock_irqsave()' in 'owl_dma_get_pchan()'.

However, according to Manivannan Sadhasivam, 'pchan->lock' was supposed
to only protect 'pchan->vchan' while 'od->lock' does a similar job in
'owl_dma_terminate_pchan()'.

Therefore, this patch substitutes 'pchan->lock' with 'od->lock' and
removes the 'lock' attribute in 'owl_dma_pchan' struct.

Fixes: 47e20577c24d ("dmaengine: Add Actions Semi Owl family S900 DMA
driver")

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxx>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
Acked-by: Andreas FÃrber <afaerber@xxxxxxx>
---
Changes in v4:
* Change patch title from 'dma: actions: Fix lockdep splat for owl-dma'
  to 'dmaengine: owl: Use correct lock in owl_dma_get_pchan()'
* Add Fixes and Acked-by tags in the commit message

Changes in v3:
* Get rid of the kerneldoc comment for the removed struct attribute
* Add the Reviewed-by tag in the commit message

Changes in v2:
* Improve the fix as suggested by Manivannan Sadhasivam: substitute
  'pchan->lock' with 'od->lock' and get rid of the 'lock' attribute in
  'owl_dma_pchan' struct
* Update the commit message to reflect the changes

 drivers/dma/owl-dma.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/owl-dma.c b/drivers/dma/owl-dma.c
index c683051257fd..66ef70b00ec0 100644
--- a/drivers/dma/owl-dma.c
+++ b/drivers/dma/owl-dma.c
@@ -175,13 +175,11 @@ struct owl_dma_txd {
  * @id: physical index to this channel
  * @base: virtual memory base for the dma channel
  * @vchan: the virtual channel currently being served by this physical channel
- * @lock: a lock to use when altering an instance of this struct
  */
 struct owl_dma_pchan {
 	u32			id;
 	void __iomem		*base;
 	struct owl_dma_vchan	*vchan;
-	spinlock_t		lock;
 };
 
 /**
@@ -437,14 +435,14 @@ static struct owl_dma_pchan *owl_dma_get_pchan(struct owl_dma *od,
 	for (i = 0; i < od->nr_pchans; i++) {
 		pchan = &od->pchans[i];
 
-		spin_lock_irqsave(&pchan->lock, flags);
+		spin_lock_irqsave(&od->lock, flags);
 		if (!pchan->vchan) {
 			pchan->vchan = vchan;
-			spin_unlock_irqrestore(&pchan->lock, flags);
+			spin_unlock_irqrestore(&od->lock, flags);
 			break;
 		}
 
-		spin_unlock_irqrestore(&pchan->lock, flags);
+		spin_unlock_irqrestore(&od->lock, flags);
 	}
 
 	return pchan;
-- 
2.26.2