linux-kernel - Re: [PATCH] net: stmmac: fix FPE events losing

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Date:   Tue, 14 Nov 2023 23:13:53 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Jianheng Zhang <Jianheng.Zhang@...opsys.com>
Cc:     Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Tan Tee Min <tee.min.tan@...el.com>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        Voon Weifeng <weifeng.voon@...el.com>,
        Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: stmmac: fix FPE events losing

On Tue, Nov 14, 2023 at 11:07:34AM +0000, Jianheng Zhang wrote:
> The 32-bit access of register MAC_FPE_CTRL_STS may clear the FPE status
> bits unexpectedly. Use 8-bit access for MAC_FPE_CTRL_STS control bits to
> avoid unexpected access of MAC_FPE_CTRL_STS status bits that can reduce
> the FPE handshake retries.
> 
> The bit[19:17] of register MAC_FPE_CTRL_STS are status register bits.
> Those bits are clear on read (or write of 1 when RCWE bit in
> MAC_CSR_SW_Ctrl register is set). Using 32-bit access for
> MAC_FPE_CTRL_STS control bits makes side effects that clear the status
> bits. Then the stmmac interrupt handler missing FPE event status and
> leads to FPE handshake failure and retries.

Is it possible to call the core of stmmac_fpe_irq_status() to extract
the information from these bits and then call
stmmac_fpe_event_status()?

Alternatively, can you actually set RCWE in MAC_CSR_SW_Ctrl and add a
mask to dwmac5_fpe_configure() etc so they don't write 1 to these
bits? That seems safer than assuming 8 bit reads work.

      Andrew