linux-kernel - Re: [PATCH v3 3/3] staging: vt6655: Replace VNSvInPortD with ioread32

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Message-ID: <YmwDZi3mmWRHzKAT@kroah.com>
Date:   Fri, 29 Apr 2022 17:25:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Philipp Hortmann <philipp.g.hortmann@...il.com>
Cc:     Forest Bond <forest@...ttletooquiet.net>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] staging: vt6655: Replace VNSvInPortD with ioread32

On Fri, Apr 29, 2022 at 05:18:28PM +0200, Philipp Hortmann wrote:
> On 4/27/22 07:55, Greg Kroah-Hartman wrote:
> > > MACvRegBitsOn(iobase, MAC_REG_TFTCTL, TFTCTL_TSFCNTRRD);
> > >   	for (ww = 0; ww < W_MAX_TIMEOUT; ww++) {
> > > @@ -753,8 +754,9 @@ bool CARDbGetCurrentTSF(struct vnt_private *priv, u64 *pqwCurrTSF)
> > >   	}
> > >   	if (ww == W_MAX_TIMEOUT)
> > >   		return false;
> > > -	VNSvInPortD(iobase + MAC_REG_TSFCNTR, (u32 *)pqwCurrTSF);
> > > -	VNSvInPortD(iobase + MAC_REG_TSFCNTR + 4, (u32 *)pqwCurrTSF + 1);
> > > +	low = ioread32(iobase + MAC_REG_TSFCNTR);
> > > +	high = ioread32(iobase + MAC_REG_TSFCNTR + 4);
> > > +	*pqwCurrTSF = low + ((u64)high << 32);
> > Are you_sure_  this is doing the same thing?
> > 
> 
> To compare I used the following code:
> VNSvInPortD(iobase + MAC_REG_TSFCNTR, (u32 *)pqwCurrTSF);
> VNSvInPortD(iobase + MAC_REG_TSFCNTR + 4, (u32 *)pqwCurrTSF + 1);
> dev_info(&priv->pcid->dev, "CARDbGetCurrentTSF *pqwCurrTSF: %llx",
> *pqwCurrTSF);
> low = ioread32(iobase + MAC_REG_TSFCNTR);
> high = ioread32(iobase + MAC_REG_TSFCNTR + 4);
> dev_info(&priv->pcid->dev, "CARDbGetCurrentTSF low/high: %llx", low +
> ((u64)high << 32));
> 
> Output:
> vt6655 0000:01:05.0: CARDbGetCurrentTSF *pqwCurrTSF: 1155ba
> vt6655 0000:01:05.0: CARDbGetCurrentTSF low/high:    1155ba
> vt6655 0000:01:05.0: CARDbGetCurrentTSF *pqwCurrTSF: 35d7cbd7c
> vt6655 0000:01:05.0: CARDbGetCurrentTSF low/high:    35d7cbd7c
> vt6655 0000:01:05.0: CARDbGetCurrentTSF *pqwCurrTSF: 35d7cbd8a
> vt6655 0000:01:05.0: CARDbGetCurrentTSF low/high:    35d7cbd8a
> 
> So no different results for numbers larger than 32 Bit.

And for a big endian system?  Do you get the same result?

> The pqwCurrTSF is a microsecond counter running in the WLAN Router:
> At a later Measurement I got the following values:
> 269 seconds later: 0x3 6d89 fd91 -> 269.30 seconds
> 15 minutes later: 0x3 6d89 fd91 -> 15.54 minutes
> 8:38 hours later: 0xa 9787 ad91 -> 8.62 hours
> 
> So both methods work on a AMD64 processor.
> 
> > Adding 1 to a u64 pointer increments it by a full u64.  So I guess the
> > cast to u32 * moves it only by a u32?  Hopefully?  That's messy.
> 
> That is the reason why I wanted to change this.
> 
> > Why not keep the current mess and do:
> > 	pqwCurrTSF = ioread32(iobase + MAC_REG_TSFCNTR);
> > 	((u32 *)pqwCurTSF + 1) = ioread32(iobase + MAC_REG_TSFCNTR + 4);
> > Or does that not compile?
> 
> drivers/staging/vt6655/card.c:760:13: warning: assignment to ‘u64 *’ {aka
> ‘long long unsigned int *’} from ‘unsigned int’ makes pointer from integer
> without a cast [-Wint-conversion]
>   760 |  pqwCurrTSF = ioread32(iobase + MAC_REG_TSFCNTR);
>       |             ^
> drivers/staging/vt6655/card.c:761:26: error: lvalue required as left operand
> of assignment
>   761 |  ((u32 *)pqwCurrTSF + 1) = ioread32(iobase + MAC_REG_TSFCNTR + 4);
>       |                          ^
> 
> This compiles:
> 	*(u32 *)pqwCurrTSF = ioread32(iobase + MAC_REG_TSFCNTR);
> 	*((u32 *)pqwCurrTSF + 1) = ioread32(iobase + MAC_REG_TSFCNTR + 4);

Heh, I just guessed :)

> Log:
> vt6655 0000:01:05.0: CARDbGetCurrentTSF *pqwCurrTSF: 178f41d90
> vt6655 0000:01:05.0: CARDbGetCurrentTSF with ioread: 178f41d90
> 
> Ick, how about:
> > 	u32 *temp = (u32 *)pqwCurTSF;
> > 
> > 	temp = ioread32(iobase + MAC_REG_TSFCNTR);
> > 	temp++;
> > 	temp = ioread32(iobase + MAC_REG_TSFCNTR + 4);
> 
> This is working:
> 	u32 *temp = (u32 *)pqwCurrTSF;
> 
> 	*temp = ioread32(iobase + MAC_REG_TSFCNTR);
> 	temp++;
> 	*temp = ioread32(iobase + MAC_REG_TSFCNTR + 4);

Nice!

thanks for testing,

greg k-h