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SubjectRe: [PATCH] nvme: explicitly disable APST on quirked devices
On Sat, Jun 24, 2017 at 1:17 AM, Andy Lutomirski <luto@kernel.org> wrote:
> On Thu, Jun 22, 2017 at 11:19 PM, Kai-Heng Feng
> <kai.heng.feng@canonical.com> wrote:
>> A user reports APST is enabled, even when the NVMe is quirked or with
>> option "default_ps_max_latency_us=0".
>>
>> The current logic will not set APST if the device is quirked. But the
>> NVMe in question will enable APST automatically.
>>
>> Separate the logic "apst is supported" and "to enable apst", so we can
>> use the latter one to explicitly disable APST at initialiaztion.
>>
>> BugLink: https://bugs.launchpad.net/bugs/1699004
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
>> ---
>> drivers/nvme/host/core.c | 25 +++++++++++++++++--------
>> drivers/nvme/host/nvme.h | 1 +
>> 2 files changed, 18 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
>> index 0ddd6b9af7fc..c459d15d18f5 100644
>> --- a/drivers/nvme/host/core.c
>> +++ b/drivers/nvme/host/core.c
>> @@ -1477,6 +1477,14 @@ static void nvme_configure_apst(struct nvme_ctrl *ctrl)
>> if (!ctrl->apsta)
>> return;
>>
>> + if (!ctrl->apst_enabled) {
>> + if (ctrl->state == NVME_CTRL_NEW ||
>> + ctrl->state == NVME_CTRL_RESETTING)
>> + dev_info(ctrl->device, "Disable APST at initialization\n");
>> + else
>> + return;
>> + }
>> +
>
> Is this change really necessary? ISTM that, if we want to optimize
> the case where we're not changing anything, we should do it more
> generally.

Do you mean combining the check on ctrl->apsta and ctrl->apst_enabled
if we do nothing and just want to return?

>
>> if (ctrl->npss > 31) {
>> dev_warn(ctrl->device, "NPSS is invalid; not using APST\n");
>> return;
>> @@ -1486,7 +1494,7 @@ static void nvme_configure_apst(struct nvme_ctrl *ctrl)
>> if (!table)
>> return;
>>
>> - if (ctrl->ps_max_latency_us == 0) {
>> + if (ctrl->ps_max_latency_us == 0 || !ctrl->apst_enabled) {
>> /* Turn off APST. */
>> apste = 0;
>> dev_dbg(ctrl->device, "APST disabled\n");
>> @@ -1653,7 +1661,7 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
>> u64 cap;
>> int ret, page_shift;
>> u32 max_hw_sectors;
>> - u8 prev_apsta;
>> + bool prev_apst_enabled;
>>
>> ret = ctrl->ops->reg_read32(ctrl, NVME_REG_VS, &ctrl->vs);
>> if (ret) {
>> @@ -1721,16 +1729,17 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
>> ctrl->kas = le16_to_cpu(id->kas);
>>
>> ctrl->npss = id->npss;
>> - prev_apsta = ctrl->apsta;
>> + ctrl->apsta = id->apsta;
>
> So ctrl->apsta now means, literally, is APSTA set in the features.
> This seems good.
>
>> + prev_apst_enabled = ctrl->apst_enabled;
>> if (ctrl->quirks & NVME_QUIRK_NO_APST) {
>> if (force_apst && id->apsta) {
>> dev_warn(ctrl->device, "forcibly allowing APST due to nvme_core.force_apst -- use at your own risk\n");
>> - ctrl->apsta = 1;
>> + ctrl->apst_enabled = true;
>> } else {
>> - ctrl->apsta = 0;
>> + ctrl->apst_enabled = false;
>> }
>> } else {
>> - ctrl->apsta = id->apsta;
>> + ctrl->apst_enabled = true;
>
> Shouldn't this be ctrl->apst_enabled = id->apsta?
>
> The way you have it could cause us to do the wrong thing if id->apsta
> somehow changes between identifications.

You are right. It should be initialized with id->apsta.

I am curious though, when does NVMe do multiple identifications?

>
>
>> memcpy(ctrl->psd, id->psd, sizeof(ctrl->psd));
>>
>> @@ -1760,9 +1769,9 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
>>
>> kfree(id);
>>
>> - if (ctrl->apsta && !prev_apsta)
>> + if (ctrl->apst_enabled && !prev_apst_enabled)
>> dev_pm_qos_expose_latency_tolerance(ctrl->device);
>> - else if (!ctrl->apsta && prev_apsta)
>> + else if (!ctrl->apst_enabled && prev_apst_enabled)
>> dev_pm_qos_hide_latency_tolerance(ctrl->device);
>
> This is also wrong unless you make the change above, I think.

Thanks, I'll address these issues on later version.

>
> --Andy

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