From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Parker Newman <parker@finest.io>
Cc: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
"Parker Newman" <pnewman@connecttech.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-serial <linux-serial@vger.kernel.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Jiri Slaby" <jirislaby@kernel.org>
Subject: Re: [PATCH v1 11/13] serial: 8250_exar: Use BIT() in exar_ee_read()
Date: Mon, 6 May 2024 11:37:29 +0300 [thread overview]
Message-ID: <ZjiWyYlfd7NdevFq@smile.fi.intel.com> (raw)
In-Reply-To: <20240503145633.1ad55378@SWDEV2.connecttech.local>
On Fri, May 03, 2024 at 02:56:33PM -0400, Parker Newman wrote:
> On Fri, 3 May 2024 18:35:45 +0300
> Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> > On Fri, May 03, 2024 at 10:26:32AM -0400, Parker Newman wrote:
> > > On Thu, 2 May 2024 20:20:01 +0300
> > > Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> > > > 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.
> > > >
> > >
> > > I just tested this and Ilpo is correct, the read loop portion is backwards as
> > > expected. This is the corrected loop:
> > >
> > > // Read data 1 bit at a time
> > > for (i = UART_EXAR_REGB_EE_DATA_SIZE; i >= 0; i--) {
> > > if (exar_ee_read_bit(priv))
> > > data |= BIT(i);
> > > }
> > >
> > > I know this looks wrong because its looping from 16->0 rather than the
> > > more intuitive 15->0 for a 16bit value. This is actually correct however
> > > because according to the AT93C46D datasheet there is always dummy 0 bit
> > > before the actual 16 bits of data.
> > >
> > > I hope that helps,
> >
> > Yes, it helps and means that we need that comment to be added to the code. Is
> > it the same applicable to the write part above (for address)? Because AFAIU
> > mine is one bit longer than yours. Maybe in the original code is a bug? Have
> > you tried to read high addresses?
>
> The address portion is 6 bits, nothing extra, so what you have is correct.
>
> The original code was legacy, I cleaned it up but didn't change those loops.
>
> Your method works out the the same number of bits as the legacy method
> which sets bit 5 and has to shift right 6 times to get i = 0 which ends the loop.
Okay, thank your for confirming the correctness of a new code!
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2024-05-06 8:37 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-02 14:43 [PATCH v1 00/13] serial: 8250_exar: Clean up the driver Andy Shevchenko
2024-05-02 14:43 ` [PATCH v1 01/13] serial: 8250_exar: Don't return positive values as error codes Andy Shevchenko
2024-05-02 14:43 ` [PATCH v1 02/13] serial: 8250_exar: Describe all parameters in kernel doc Andy Shevchenko
2024-05-02 14:43 ` [PATCH v1 03/13] serial: 8250_exar: Kill CTI_PCI_DEVICE() Andy Shevchenko
2024-05-02 15:13 ` Parker Newman
2024-05-02 15:29 ` Andy Shevchenko
2024-05-02 15:36 ` Parker Newman
2024-05-02 15:43 ` Andy Shevchenko
2024-05-02 15:54 ` Parker Newman
2024-05-02 15:59 ` Andy Shevchenko
2024-05-02 14:43 ` [PATCH v1 04/13] serial: 8250_exar: Use PCI_SUBVENDOR_ID_IBM for subvendor ID Andy Shevchenko
2024-05-02 14:43 ` [PATCH v1 05/13] serial: 8250_exar: Trivia typo fixes Andy Shevchenko
2024-05-02 14:44 ` [PATCH v1 06/13] serial: 8250_exar: Extract cti_board_init_osc_freq() helper Andy Shevchenko
2024-05-02 14:44 ` [PATCH v1 07/13] serial: 8250_exar: Kill unneeded ->board_init() Andy Shevchenko
2024-05-02 14:44 ` [PATCH v1 08/13] serial: 8250_exar: Decrease indentation level Andy Shevchenko
2024-05-02 14:44 ` [PATCH v1 09/13] serial: 8250_exar: Return directly from switch-cases Andy Shevchenko
2024-05-02 14:44 ` [PATCH v1 10/13] serial: 8250_exar: Switch to use dev_err_probe() Andy Shevchenko
2024-05-02 14:44 ` [PATCH v1 11/13] serial: 8250_exar: Use BIT() in exar_ee_read() Andy Shevchenko
2024-05-02 16:08 ` Ilpo Järvinen
2024-05-02 17:20 ` Andy Shevchenko
2024-05-03 14:26 ` Parker Newman
2024-05-03 15:35 ` Andy Shevchenko
2024-05-03 18:56 ` Parker Newman
2024-05-06 8:37 ` Andy Shevchenko [this message]
2024-05-02 14:44 ` [PATCH v1 12/13] serial: 8250_exar: Make type of bit the same in exar_ee_*_bit() Andy Shevchenko
2024-05-02 14:44 ` [PATCH v1 13/13] serial: 8250_exar: Keep the includes sorted Andy Shevchenko
2024-05-02 15:46 ` [PATCH v1 00/13] serial: 8250_exar: Clean up the driver Parker Newman
2024-05-02 16:01 ` Andy Shevchenko
2024-05-02 16:08 ` Parker Newman
2024-05-02 17:22 ` Andy Shevchenko
2024-05-02 17:49 ` Parker Newman
2024-05-02 18:01 ` Andy Shevchenko
2024-05-03 12:36 ` Parker Newman
2024-05-03 14:47 ` Parker Newman
2024-05-03 15:33 ` Andy Shevchenko
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