linux-kernel - Re: [PATCH v1 11/13] serial: 8250_exar: Use BIT() in exar_ee

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Date: Thu, 2 May 2024 20:20:01 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Parker Newman <pnewman@...necttech.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-serial <linux-serial@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH v1 11/13] serial: 8250_exar: Use BIT() in exar_ee_read()

On Thu, May 02, 2024 at 07:08:21PM +0300, Ilpo Järvinen wrote:
> On Thu, 2 May 2024, Andy Shevchenko wrote:

..

> >  	// Send address to read from
> > -	for (i = 1 << (UART_EXAR_REGB_EE_ADDR_SIZE - 1); i; i >>= 1)
> > -		exar_ee_write_bit(priv, (ee_addr & i));
> > +	for (i = UART_EXAR_REGB_EE_ADDR_SIZE - 1; i >= 0; i--)
> > +		exar_ee_write_bit(priv, ee_addr & BIT(i));
> >  
> >  	// Read data 1 bit at a time
> >  	for (i = 0; i <= UART_EXAR_REGB_EE_DATA_SIZE; i++) {
> > -		data <<= 1;
> > -		data |= exar_ee_read_bit(priv);
> > +		if (exar_ee_read_bit(priv))
> > +			data |= BIT(i);
> 
> Does this end up reversing the order of bits? In the original, data was left
> shifted which moved the existing bits and added the lsb but the replacement
> adds highest bit on each iteration?

Oh, seems a good catch!

I was also wondering, but missed this somehow. Seems the EEPROM is in BE mode,
so two loops has to be aligned.

-- 
With Best Regards,
Andy Shevchenko