gem: use an explicit dsb sy in the polling RX path

[dgarske]

gem_eth_poll() in src/port/amd/ip/gem_rx_poll.c issues dsb with no option. That is valid ARMv7-A, where the option defaults to SY, but not AArch64, where it is mandatory - so the file fails to assemble with Error: missing immediate expression at operand 1 -- 'dsb' as soon as an AArch64 board selects the polling RX model. Both barriers become dsb sy, which both architectures accept.

This is a no-op for the existing ARMv7 user: boards/zynq7000 builds this file for a Cortex-A9, and the resulting gem_rx_poll.o is byte-identical before and after the change (f57ff04f, dsb sy, at all five sites).

Validated by building boards/zynq7000 for armv7-a and compiling the same file for AArch64, and on hardware: the zynq7000 demo on a ZC702 links at auto-negotiation, binds a DHCP lease, answers ping, and completes a UDP echo round trip through this RX path.

[Copilot]

🟡 Changes recommended

Reconcile the file’s ARMv7 build path with the stated AArch64 target.

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Pull request overview

Updates GEM RX polling barriers from bare dsb to dsb sy for AArch64 compatibility.

Changes:

• Replaces both inline barriers in the polling RX path.
• Preserves full-system barrier semantics.

File summaries

File	Summary
src/port/amd/ip/gem_rx_poll.c	Updates RX descriptor memory barriers.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.