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Revert "EmbeddedPkg/Lan9118Dxe: use MemoryFence"

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Commit a4626006bb ("EmbeddedPkg/Lan9118Dxe: use MemoryFence")
replaced some stalls with memory fences, on the presumption that these
were erroneously being used to order memory accesses. However, this was
not the case.

LAN9118 devices require a timing delay between state-changing
reads/writes and subsequent reads, as updates to the register file are
asynchronous and the effects of state-changes are not immediately
visible to subsequent reads.

This delay cannot be ensured through the use of memory barriers, which
only enforce observable ordering, and not timing. Thus, converting these
stalls to memory fences was erroneous, and may result in stale values
being read.

This reverts commit a4626006bb.

Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Ryan Harkin <ryan.harkin@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
This commit is contained in:
Mark Rutland
2016-05-06 18:19:06 +01:00
committed by Ard Biesheuvel
parent d1ec2b2f78
commit 28f52b9fae
2 changed files with 23 additions and 26 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
EmbeddedPkg/Drivers/Lan9118Dxe/Lan9118Dxe.c
View File

@@ -307,7 +307,8 @@ SnpInitialize (
// Write the current configuration to the register
MmioWrite32 (LAN9118_PMT_CTRL, PmConf);
MemoryFence();
gBS->Stall (LAN9118_STALL);
gBS->Stall (LAN9118_STALL);
// Configure GPIO and HW
Status = ConfigureHardware (HW_CONF_USE_LEDS, Snp);
@@ -430,7 +431,7 @@ SnpReset (
// Write the current configuration to the register
MmioWrite32 (LAN9118_PMT_CTRL, PmConf);
MemoryFence();
gBS->Stall (LAN9118_STALL);
// Reactivate the LEDs
Status = ConfigureHardware (HW_CONF_USE_LEDS, Snp);
@@ -445,7 +446,7 @@ SnpReset (
HwConf |= HW_CFG_TX_FIFO_SIZE(gTxBuffer); // assign size chosen in SnpInitialize
MmioWrite32 (LAN9118_HW_CFG, HwConf); // Write the conf
MemoryFence();
gBS->Stall (LAN9118_STALL);
}
// Enable the receiver and transmitter and clear their contents
@@ -700,7 +701,7 @@ SnpReceiveFilters (
// Write the options to the MAC_CSR
//
IndirectMACWrite32 (INDIRECT_MAC_INDEX_CR, MacCSRValue);
MemoryFence();
gBS->Stall (LAN9118_STALL);
//
// If we have to retrieve something, start packet reception.