Re: [PATCH v2 2/3] fpga: region: Add fpga-region 'power-domains' property

On Mon, Jul 18, 2022 at 06:46:32AM +0000, Manne, Nava kishore wrote:

Hi Yilun,

	Please find my response inline.

quoted

-----Original Message-----
From: Xu Yilun <yilun.xu@intel.com>
Sent: Friday, June 24, 2022 9:58 PM
To: Nava kishore Manne <redacted>
Cc: mdf@kernel.org; hao.wu@intel.com; trix@redhat.com;
robh+dt@kernel.org; krzysztof.kozlowski+dt@linaro.org;
michal.simek@xilinx.com; linux-fpga@vger.kernel.org;
devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-
kernel@lists.infradead.org; git@xilinx.com; Rob Herring [off-list ref]
Subject: Re: [PATCH v2 2/3] fpga: region: Add fpga-region 'power-domains'
property

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On Mon, May 23, 2022 at 07:15:16PM +0530, Nava kishore Manne wrote:

quoted

Add fpga-region 'power-domains' property to allow to handle the
FPGA/PL power domains.

Signed-off-by: Nava kishore Manne <redacted>
Acked-by: Rob Herring <robh@kernel.org>
---
Changes for v2:
              - Updated power-domains description.

 .../devicetree/bindings/fpga/fpga-region.txt       | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Documentation/devicetree/bindings/fpga/fpga-region.txt

b/Documentation/devicetree/bindings/fpga/fpga-region.txt
index 7d3515264838..f299c3749505 100644

--- a/Documentation/devicetree/bindings/fpga/fpga-region.txt
+++ b/Documentation/devicetree/bindings/fpga/fpga-region.txt

@@ -196,6 +196,20 @@ Optional properties:
 - config-complete-timeout-us : The maximum time in microseconds time

for the

quoted

      FPGA to go to operating mode after the region has been programmed.
 - child nodes : devices in the FPGA after programming.
+- power-domains : A phandle and power domain specifier pair to the

power domain

quoted

+     which is responsible for turning on/off the power to the FPGA/PL

region.

Could you help explain what is PL?

quoted

+Example:
+     fpga_full: fpga-full {
+                compatible = "fpga-region";
+                fpga-mgr = <&zynqmp_pcap>;
+                #address-cells = <2>;
+                #size-cells = <2>;
+                ranges;
+                power-domains = <&zynqmp_firmware PL_PD>;
+        };
+
+     The PL_PD power domain will be turned on before loading the
+bitstream and turned off while removing/unloading the bitstream using

overlays.

I think the single power-domain may not cover some use cases that of-fpga-
region driver supports.

I am not sure which use case you are talking about. Can you please point me the exact use case here?
  

quoted

It is possible there are already devices in fpga-region
for static OF tree, or an overlay with no 'firmware-name' but 'external-fpga-
config'. In these cases power domains may still be needed, is it?

It's an optional property user can decide whether he needs this support or not for 'external-fpga-config
Use case. 

If an external-fpga-config FPGA region needs to enable a power domain before
sub devices population, how could it config the DT? I assume in this
patch "power-domains" property is only used before & after
reconfiguration but external-fpga-config FPGA region may need no
reconfiguration.

quoted

Another case is the fpga-region may need multiple power domains?

In our use case full region and relevant partial regions have different power domains and
this patch is capable of handle different power domain regions (full and partial regions)

If a FPGA region needs 2 or more power domains for partial reconfiguration,
how could we find out and enable them all?

From the 2 cases, I see as a generic driver, there may be need to enable
different power domains at different moments. And I'm afraid a simple
implementation of pm_runtime_get before reconfiguration may limit the
usage of "power-domains" property for of-fpga-region.

Thanks,
Yilun

quoted

Since the of-fpga-region driver is a generic fpga-region driver, we may
investigate more for a compatible power-domain solution.

Please share your thoughts here we will try to align with it.

Regards,
Navakishore.

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