2018-05-03 04:46:20

by Alistair Strachan

Subject: [PATCH 1/3] staging: Android: vsoc: Create wc kernel mapping for region shm.

Map the region shm as write-combining instead of uncachable.

Cc: Greg Kroah-Hartman <[email protected]>
Cc: Arve Hjønnevåg <[email protected]>
Cc: Todd Kjos <[email protected]>
Cc: Martijn Coenen <[email protected]>
Cc: Greg Hartman <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Alistair Strachan <[email protected]>
---
drivers/staging/android/TODO | 1 -
drivers/staging/android/vsoc.c | 4 +---
2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/staging/android/TODO b/drivers/staging/android/TODO
index 2ea6f97b8f0f..ebd6ba3ae02e 100644
--- a/drivers/staging/android/TODO
+++ b/drivers/staging/android/TODO
@@ -18,7 +18,6 @@ vsoc.c, uapi/vsoc_shm.h
waiting threads. We should eventually use multiple queues and select the
queue based on the region.
- Add debugfs support for examining the permissions of regions.
- - Use ioremap_wc instead of ioremap_nocache.
- Remove VSOC_WAIT_FOR_INCOMING_INTERRUPT ioctl. This functionality has been
superseded by the futex and is there for legacy reasons.

diff --git a/drivers/staging/android/vsoc.c b/drivers/staging/android/vsoc.c
index 587c66d709b9..794137b7751f 100644
--- a/drivers/staging/android/vsoc.c
+++ b/drivers/staging/android/vsoc.c
@@ -802,9 +802,7 @@ static int vsoc_probe_device(struct pci_dev *pdev,

dev_info(&pdev->dev, "shared memory @ DMA %p size=0x%zx\n",
(void *)vsoc_dev.shm_phys_start, vsoc_dev.shm_size);
- /* TODO(ghartman): ioremap_wc should work here */
- vsoc_dev.kernel_mapped_shm = ioremap_nocache(
- vsoc_dev.shm_phys_start, vsoc_dev.shm_size);
+ vsoc_dev.kernel_mapped_shm = pci_iomap_wc(pdev, SHARED_MEMORY_BAR, 0);
if (!vsoc_dev.kernel_mapped_shm) {
dev_err(&vsoc_dev.dev->dev, "cannot iomap region\n");
vsoc_remove_device(pdev);

2018-05-03 05:12:29

by Joel Fernandes

Subject: Re: [kernel-team] [PATCH 1/3] staging: Android: vsoc: Create wc kernel mapping for region shm.

On Wed, May 2, 2018 at 9:45 PM 'Alistair Strachan' via kernel-team <
[email protected]> wrote:

> Map the region shm as write-combining instead of uncachable.


I think more commit message is needed. Why is this done, what does it fix,
etc. Its hard to know what the improvement is without a cover-letter either.

I am assuming the improvement is in performance by using the
write-combining mode.

thanks,

- Joel