linux-kernel - Re: [PATCH 1/1] mct_u232: added _ioctl, _msr_to_icount and _get

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Date:	Mon, 27 Dec 2010 12:55:38 -0800 (PST)
From:	Tsozik <tsozik@...oo.com>
To:	Pete Zaitcev <zaitcev@...hat.com>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mct_u232: added _ioctl, _msr_to_icount and _get_icount functions

Pete,

You're absolutely right. My apology again, I re-checked values of MSR masks used to update icount counters and they all belong to upper MSR nibble, so they indeed track changes (not states). I took out counter increments from mct_u232_msr_to_state function and encapsulated them in the newly defined mct_u232_msr_to_icount function, effectively leaving the previous implementation of mct_u232_msr_to_state function intact. mct_u232_msr_to_icount uses delta nibble to track state changes. RM-60 testing showed the same levels as measured by PDM-2 in close proximity to RM-60. Please let me know if anything else needs to be corrected to roll this out,

Thank you again for your expertise,
 Vadim.

--- On Mon, 12/27/10, Pete Zaitcev <zaitcev@...hat.com> wrote:

> From: Pete Zaitcev <zaitcev@...hat.com>
> Subject: Re: [PATCH 1/1] mct_u232: added _ioctl and _get_icount functions
> To: "Tsozik" <tsozik@...oo.com>
> Cc: "Greg Kroah-Hartman" <gregkh@...e.de>, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
> Date: Monday, December 27, 2010, 12:08 PM
> On Sun, 26 Dec 2010 22:34:23 -0800
> (PST)
> Tsozik <tsozik@...oo.com>
> wrote:
> 
> > Usually MSR contains information about both states
> which are raised and
> > states which are changed. It looks like we use upper
> MSR nibble which
> > contains information about 4 states which were raised,
> not lower MSR
> > nibble which contains information about 4 states which
> were changed.
> 
> Sure, I know how typical UART works. Does the MCT device
> deliver the
> change states? If it does and you want to use those, go
> ahead.
> 
> > I also researched implementations under usb/serial and
> saw that all of
> > them are rely on the current states (not change
> states) to increment
> > the respective counter variables.
> 
> Here's drivers/usb/serial/io_edgeport.c:
> 
> static void handle_new_msr(struct edgeport_port *edge_port,
> __u8 newMsr)
> {
>     struct  async_icount *icount;
> 
>     dbg("%s %02x", __func__, newMsr);
> 
>     if (newMsr & (EDGEPORT_MSR_DELTA_CTS
> | EDGEPORT_MSR_DELTA_DSR |
>            
> EDGEPORT_MSR_DELTA_RI | EDGEPORT_MSR_DELTA_CD)) {
>         icount =
> &edge_port->icount;
> 
>         /* update input line
> counters */
>         if (newMsr &
> EDGEPORT_MSR_DELTA_CTS)
>            
> icount->cts++;
>         if (newMsr &
> EDGEPORT_MSR_DELTA_DSR)
>            
> icount->dsr++;
>         if (newMsr &
> EDGEPORT_MSR_DELTA_CD)
>            
> icount->dcd++;
>         if (newMsr &
> EDGEPORT_MSR_DELTA_RI)
>            
> icount->rng++;
>        
> wake_up_interruptible(&edge_port->delta_msr_wait);
>     }
> 
> Looks like it counts changes to me. And in any case, the
> gold standard
> is in drivers/serial/8250.c:
> 
> static unsigned int check_modem_status(struct
> uart_8250_port *up)
> {
>     unsigned int status = serial_in(up,
> UART_MSR);
> 
>     status |= up->msr_saved_flags;
>     up->msr_saved_flags = 0;
>     if (status & UART_MSR_ANY_DELTA
> && up->ier & UART_IER_MSI &&
>         up->port.state != NULL)
> {
>         if (status &
> UART_MSR_TERI)
>            
> up->port.icount.rng++;
>         if (status &
> UART_MSR_DDSR)
>            
> up->port.icount.dsr++;
>         if (status &
> UART_MSR_DDCD)
>            
> uart_handle_dcd_change(&up->port, status &
> UART_MSR_DCD);
>         if (status &
> UART_MSR_DCTS)
>            
> uart_handle_cts_change(&up->port, status &
> UART_MSR_CTS);
> 
>        
> wake_up_interruptible(&up->port.state->port.delta_msr_wait);
>     }
> 
> I only proposed accomplishing the same result by comparing
> states
> in place of relying on hardware change reports like both of
> the
> above do.
> 
> -- Pete
>


      
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