linux-kernel - Re: [PATCH] net: stmmac: mmc_core: Assign, don't add interrupt registers

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Date: Fri, 16 Feb 2024 21:24:01 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Florian Fainelli <f.fainelli@...il.com>, 
	Jesper Nilsson <jesper.nilsson@...s.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>, 
	Jose Abreu <joabreu@...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>, 
	netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, kernel@...s.com
Subject: Re: [PATCH] net: stmmac: mmc_core: Assign, don't add interrupt
 registers

On Fri, Feb 16, 2024 at 09:13:51AM -0800, Florian Fainelli wrote:
> On 2/16/24 07:24, Jesper Nilsson wrote:
> > The MMC IPC interrupt status and interrupt mask registers are of
> > little use as Ethernet statistics, but incrementing counters
> > based on the current interrupt and interrupt mask registers
> > makes them worse than useless.
> > 
> > For example, if the interrupt mask is set to 0x08420842,
> > the current code will increment by that amount each iteration,
> > leading to the following sequence of nonsense:
> > 
> > mmc_rx_ipc_intr_mask: 969816526
> > mmc_rx_ipc_intr_mask: 1108361744
> > 
> > Change the increment to a straight assignment to make the
> > statistics at least nominally useful.
> > 
> > Signed-off-by: Jesper Nilsson <jesper.nilsson@...s.com>
> > ---
> >   drivers/net/ethernet/stmicro/stmmac/mmc_core.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/mmc_core.c b/drivers/net/ethernet/stmicro/stmmac/mmc_core.c
> > index 6a7c1d325c46..6051a22b3cec 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/mmc_core.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/mmc_core.c
> > @@ -280,8 +280,8 @@ static void dwmac_mmc_read(void __iomem *mmcaddr, struct stmmac_counters *mmc)
> >   	mmc->mmc_rx_vlan_frames_gb += readl(mmcaddr + MMC_RX_VLAN_FRAMES_GB);
> >   	mmc->mmc_rx_watchdog_error += readl(mmcaddr + MMC_RX_WATCHDOG_ERROR);
> >   	/* IPC */
> > -	mmc->mmc_rx_ipc_intr_mask += readl(mmcaddr + MMC_RX_IPC_INTR_MASK);
> > -	mmc->mmc_rx_ipc_intr += readl(mmcaddr + MMC_RX_IPC_INTR);
> > +	mmc->mmc_rx_ipc_intr_mask = readl(mmcaddr + MMC_RX_IPC_INTR_MASK);
> > +	mmc->mmc_rx_ipc_intr = readl(mmcaddr + MMC_RX_IPC_INTR);
> 

> So in premise I agree with the patch, that incrementing those is not the
> right way to go about them. However these registers are currently provided
> as part of the statistics set, but they should instead be accessed via the
> register dumping method.
> 
> In either case you will get at best a snapshot of those two registers at any
> given time and I suppose this can help diagnose a stuck RX condition, but
> not much more than that.

Could you please clarify why do those CSRs state need to be exposed in
the statistics anyway? Who would need such information really?
Wouldn't that be better to just drop the
stmmac_counters::{mmc_rx_ipc_intr_mask,mmc_rx_ipc_intr}
fields? Is it because of the statistics nodes are a kind of kernel
ABI? Even in that case I don't see much reason to support something
that has been absolutely useless so far seeing the nodes currently
returning basically some random values.

-Serge(y)

> -- 
> Florian
> 
>