[PATCH 2/2] drm/amdgpu: disable gfxoff when using register read interface

[Yuan, Xiaojie]

Hi Alex,

I tried on Navi14 with Gfxoff enabled (gfx in 'OFF' state when I run the test program) and used a test program to read GRBM_STATUS/CP_STAT/GB_ADDR_CONFIG via DRM_IOCTL_AMDGPU_INFO.

All read out values are valid as below (in this read cycle, I saw gfx block is first awakened and then powered off again automatically):

drm version: 3.36.0
grbm_status: 0x00003028
cp_stat: 0x00000000
gb_addr_config: 0x00000043

At least for Navi, reading register when gfxoff seems not a problem...

Test program:

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <errno.h>
#include <libdrm/drm.h>
#include <libdrm/amdgpu_drm.h>

int get_reg_val(int fd, int reg_offset, int *val)
{
        struct drm_amdgpu_info request;
        int r;

        memset(&request, 0, sizeof(request));
        request.return_pointer = (uintptr_t)val;
        request.return_size = sizeof(uint32_t);
        request.query = AMDGPU_INFO_READ_MMR_REG;
        request.read_mmr_reg.dword_offset = reg_offset;
        request.read_mmr_reg.count = 1;
        request.read_mmr_reg.instance = 0xffffffff;
        request.read_mmr_reg.flags = 0;

        r = ioctl(fd, DRM_IOCTL_AMDGPU_INFO, &request);
        if (r < 0) {
                perror("failed to read register");
                return -errno;
        }

        return 0;
}

int main(int argc, const char *argv[])
{
        const char *device = "/dev/dri/card0";
        int fd;
        int r;
        struct drm_version version;
        struct drm_auth auth;
        int cp_stat;
        int grbm_status;
        int gb_addr_config;

        fd = open(device, O_RDWR | O_CLOEXEC);
        if (fd < 0) {
                perror("failed to open device\n");
                return -errno;
        }

        memset(&version, 0, sizeof(version));

        r = ioctl(fd, DRM_IOCTL_VERSION, &version);
        if (r < 0) {
                perror("failed to get drm version");
                r = -errno;
                goto close;
        }

        printf("drm version: %d.%d.%d\n", version.version_major,
                                          version.version_minor,
                                          version.version_patchlevel);

        r = get_reg_val(fd, 0x2004, &grbm_status);
        if (r < 0)
                goto close;
        printf("grbm_status: 0x%08x\n", grbm_status);

        r = get_reg_val(fd, 0x21a0, &cp_stat);
        if (r < 0)
                goto close;
        printf("cp_stat: 0x%08x\n", cp_stat);

        r = get_reg_val(fd, 0x263e, &gb_addr_config);
        if (r < 0)
                goto close;
        printf("gb_addr_config: 0x%08x\n", gb_addr_config);

close:
        close(fd);

        return r;
}

BR,
Xiaojie

________________________________________
From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> on behalf of Yuan, Xiaojie <Xiaojie.Yuan at amd.com>
Sent: Saturday, November 16, 2019 1:02 AM
To: Alex Deucher
Cc: Deucher, Alexander; amd-gfx at lists.freedesktop.org
Subject: Re: [PATCH 2/2] drm/amdgpu: disable gfxoff when using register read interface

Yes. IIRC, some asics' amdgpu_gfx_ctrl() is implemented as synchronous (upon function returns, gfx block is guaranteed to be in power-up state). Anyway, let me confirm about that soon.

BR,
Xiaojie

> On Nov 16, 2019, at 12:52 AM, Alex Deucher <alexdeucher at gmail.com> wrote:
>
>> On Fri, Nov 15, 2019 at 11:46 AM Yuan, Xiaojie <Xiaojie.Yuan at amd.com> wrote:
>>
>> Hi Alex,
>>
>> IMHO, driver sending Disallow_Gfxoff message to SMU doesn't mean gfx block will be immediately powered up, so I'm not sure MMIO register access will be successful within this time window(maybe GRBM access will be pending until gfx block is powered up?)
>>
>> If you are not in a hurry to commit this fix, I can verify on my Navi boards next Monday.
>
> That would be great.  Maybe we can add a delay in that function to
> take that into account?
>
> Thanks!
>
> Alex
>
>>
>> BR,
>> Xiaojie
>>
>>> On Nov 15, 2019, at 12:44 AM, Alex Deucher <alexdeucher at gmail.com> wrote:
>>>
>>> When gfxoff is enabled, accessing gfx registers via MMIO
>>> can lead to a hang.
>>>
>>> Bug: https://bugzilla.kernel.org/show_bug.cgi?id=205497
>>> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
>>> ---
>>> drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c | 6 +++++-
>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
>>> index 6ddea7607ad0..5f3b3a705b29 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
>>> @@ -659,15 +659,19 @@ static int amdgpu_info_ioctl(struct drm_device *dev, void *data, struct drm_file
>>>           return -ENOMEM;
>>>       alloc_size = info->read_mmr_reg.count * sizeof(*regs);
>>>
>>> -        for (i = 0; i < info->read_mmr_reg.count; i++)
>>> +        amdgpu_gfx_off_ctrl(adev, false);
>>> +        for (i = 0; i < info->read_mmr_reg.count; i++) {
>>>           if (amdgpu_asic_read_register(adev, se_num, sh_num,
>>>                             info->read_mmr_reg.dword_offset + i,
>>>                             &regs[i])) {
>>>               DRM_DEBUG_KMS("unallowed offset %#x\n",
>>>                         info->read_mmr_reg.dword_offset + i);
>>>               kfree(regs);
>>> +                amdgpu_gfx_off_ctrl(adev, true);
>>>               return -EFAULT;
>>>           }
>>> +        }
>>> +        amdgpu_gfx_off_ctrl(adev, true);
>>>       n = copy_to_user(out, regs, min(size, alloc_size));
>>>       kfree(regs);
>>>       return n ? -EFAULT : 0;
>>> --
>>> 2.23.0
>>>
>>> _______________________________________________
>>> amd-gfx mailing list
>>> amd-gfx at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
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