Re: [PATCH V2 1/3] ufs: core: Add CPU latency QoS support for ufs driver

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On 12/6/23 05:32, Manivannan Sadhasivam wrote:
On Wed, Dec 06, 2023 at 07:32:54PM +0530, Naresh Maramaina wrote:
On 12/5/2023 10:41 PM, Bart Van Assche wrote:
On 12/4/23 21:58, Naresh Maramaina wrote:
On 12/5/2023 12:30 AM, Bart Van Assche wrote:
On 12/4/23 06:30, Maramaina Naresh wrote:
+    /* This capability allows the host controller driver to
use the PM QoS
+     * feature.
+     */
+    UFSHCD_CAP_PM_QOS                = 1 << 13,

Why does it depend on the host driver whether or not PM QoS is
enabled? Why isn't it enabled unconditionally?

For some platform vendors power KPI might be more important than
random io KPI. Hence this flag is disabled by default and can be
enabled based on platform requirement.

How about leaving this flag out unless if a host vendor asks explicitly
for this flag?

IMHO, instead of completely removing this flag, how about having
flag like "UFSHCD_CAP_DISABLE_PM_QOS" which will make PMQOS enable
by default and if some host vendor wants to disable it explicitly,
they can enable that flag.
Please let me know your opinion.

That would result in a flag that is tested but that is never set by
upstream code. I'm not sure that's acceptable.

If a vendor wants to disable this feature, then the driver has to be modified.
That won't be very convenient. So either this has to be configured through sysfs
or Kconfig if flexibility matters.

Kconfig sounds worse to me because changing any Kconfig flag requires a
modification of the Android GKI kernel.



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