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Date: Thu, 7 Dec 2017 17:26:50 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Sven Van Asbroeck <svendev@...x.com>
Cc: Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Wolfram Sang <wsa@...-dreams.de>, nsekhar@...com,
Sakari Ailus <sakari.ailus@...ux.intel.com>,
David Lechner <david@...hnology.com>,
Javier Martinez Canillas <javier@...hile0.org>,
Divagar Mohandass <divagar.mohandass@...el.com>,
devicetree@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-i2c <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH v5 1/2] at24: support eeproms that do not auto-rollover reads.
2017-12-07 15:36 GMT+01:00 Sven Van Asbroeck <svendev@...x.com>:
> Some multi-address eeproms in the at24 family may not automatically
> roll-over reads to the next slave address. On those eeproms, reads
> that straddle slave boundaries will not work correctly.
>
> Solution:
> Mark such eeproms with a flag that prevents reads straddling
> slave boundaries. Add the AT24_FLAG_NO_RDROL flag to the eeprom
> entry in the device_id table, or add 'no-read-rollover' to the
> eeprom devicetree entry.
>
> Note that I have not personally enountered an at24 chip that
> does not support read rollovers. They may or may not exist.
> However, my hardware requires this functionality because of
> a quirk.
>
> It's up to the Linux community to decide if this patch is useful/
> general enough to warrant merging.
>
> Signed-off-by: Sven Van Asbroeck <svendev@...x.com>
> ---
> drivers/misc/eeprom/at24.c | 37 +++++++++++++++++++++++++------------
> include/linux/platform_data/at24.h | 2 ++
> 2 files changed, 27 insertions(+), 12 deletions(-)
>
Hi Sven,
looks good in general, just a couple nits to fix below and it can be applied.
> diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> index 625b001..8c93ed0 100644
> --- a/drivers/misc/eeprom/at24.c
> +++ b/drivers/misc/eeprom/at24.c
> @@ -251,15 +251,6 @@ struct at24_data {
> * Slave address and byte offset derive from the offset. Always
> * set the byte address; on a multi-master board, another master
> * may have changed the chip's "current" address pointer.
> - *
> - * REVISIT some multi-address chips don't rollover page reads to
> - * the next slave address, so we may need to truncate the count.
> - * Those chips might need another quirk flag.
> - *
> - * If the real hardware used four adjacent 24c02 chips and that
> - * were misconfigured as one 24c08, that would be a similar effect:
> - * one "eeprom" file not four, but larger reads would fail when
> - * they crossed certain pages.
> */
> static struct at24_client *at24_translate_offset(struct at24_data *at24,
> unsigned int *offset)
> @@ -277,6 +268,28 @@ static struct at24_client *at24_translate_offset(struct at24_data *at24,
> return &at24->client[i];
> }
>
> +static size_t at24_adjust_read_count(struct at24_data *at24,
> + unsigned int offset, size_t count)
> +{
> + unsigned int bits;
> + size_t remainder;
Add a newline here.
> + /*
> + * In case of multi-address chips that don't rollover reads to
> + * the next slave address: truncate the count to the slave boundary,
> + * so that the read never straddles slaves.
> + */
> + if (at24->chip.flags & AT24_FLAG_NO_RDROL) {
> + bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;
There's no need for braces around the ternary operator's condition.
> + remainder = BIT(bits) - offset;
> + if (count > remainder)
> + count = remainder;
> + }
Another newline here.
> + if (count > io_limit)
> + count = io_limit;
> +
> + return count;
> +}
> +
> static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
> unsigned int offset, size_t count)
> {
> @@ -289,9 +302,7 @@ static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
> at24_client = at24_translate_offset(at24, &offset);
> regmap = at24_client->regmap;
> client = at24_client->client;
> -
> - if (count > io_limit)
> - count = io_limit;
> + count = at24_adjust_read_count(at24, offset, count);
>
> /* adjust offset for mac and serial read ops */
> offset += at24->offset_adj;
> @@ -457,6 +468,8 @@ static void at24_get_pdata(struct device *dev, struct at24_platform_data *chip)
>
> if (device_property_present(dev, "read-only"))
> chip->flags |= AT24_FLAG_READONLY;
> + if (device_property_present(dev, "no-read-rollover"))
> + chip->flags |= AT24_FLAG_NO_RDROL;
>
> err = device_property_read_u32(dev, "size", &val);
> if (!err)
> diff --git a/include/linux/platform_data/at24.h b/include/linux/platform_data/at24.h
> index 271a4e2..841bb28 100644
> --- a/include/linux/platform_data/at24.h
> +++ b/include/linux/platform_data/at24.h
> @@ -50,6 +50,8 @@ struct at24_platform_data {
> #define AT24_FLAG_TAKE8ADDR BIT(4) /* take always 8 addresses (24c00) */
> #define AT24_FLAG_SERIAL BIT(3) /* factory-programmed serial number */
> #define AT24_FLAG_MAC BIT(2) /* factory-programmed mac address */
> +#define AT24_FLAG_NO_RDROL BIT(1) /* does not auto-rollover reads to */
> + /* the next slave address */
>
> void (*setup)(struct nvmem_device *nvmem, void *context);
> void *context;
> --
> 1.9.1
>
Thanks,
Bartosz
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