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Date:   Mon, 13 Mar 2023 15:04:53 -0400
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Subject: Re: [PATCH v4] rtc: abx80x: Add nvmem support
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To:     Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc:     Alessandro Zummo <a.zummo@towertech.it>, linux-rtc@vger.kernel.org,
        linux-kernel@vger.kernel.org
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 <20230313183836e276d826@mail.local>
From:   Sean Anderson <sean.anderson@seco.com>
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On 3/13/23 14:38, Alexandre Belloni wrote:
> On 13/03/2023 11:28:30-0400, Sean Anderson wrote:
>> On 12/22/22 16:45, Sean Anderson wrote:
>> > This adds support for the 256-byte internal RAM. There are two windows
>> > which can be used to access this RAM: 64 bytes at 0x40 (the "standard"
>> > address space) and 128 bytes at 0x80 (the "alternate" address space). We
>> > use the standard address space because it is also accessible over SPI
>> > (if such a port is ever done). We are limited to 32-byte reads for SMBus
>> > compatibility, so there's no advantage to using the alternate address
>> > space.
>> > 
>> > There are some reserved bits in the EXTRAM register, and the datasheet
>> > doesn't say what to do with them. I've opted to skip a read/modify/write
>> > and just write the whole thing. If this driver is ever converted to
>> > regmap, this would be a good place to use regmap_update_bits.
>> > 
>> > Signed-off-by: Sean Anderson <sean.anderson@seco.com>
>> > ---
>> > 
>> > Changes in v4:
>> > - Remove unused variable
>> > 
>> > Changes in v3:
>> > - Use devm_rtc_nvmem_register
>> > - Remove ifdefs
>> > 
>> > Changes in v2:
>> > - Fix building on non-arm platforms
>> > 
>> >  drivers/rtc/rtc-abx80x.c | 77 ++++++++++++++++++++++++++++++++++++++++
>> >  1 file changed, 77 insertions(+)
>> > 
>> > diff --git a/drivers/rtc/rtc-abx80x.c b/drivers/rtc/rtc-abx80x.c
>> > index 9b0138d07232..74ff820f5481 100644
>> > --- a/drivers/rtc/rtc-abx80x.c
>> > +++ b/drivers/rtc/rtc-abx80x.c
>> > @@ -11,6 +11,7 @@
>> >   */
>> >  
>> >  #include <linux/bcd.h>
>> > +#include <linux/bitfield.h>
>> >  #include <linux/i2c.h>
>> >  #include <linux/module.h>
>> >  #include <linux/of_device.h>
>> > @@ -87,6 +88,16 @@
>> >  #define ABX8XX_TRICKLE_STANDARD_DIODE	0x8
>> >  #define ABX8XX_TRICKLE_SCHOTTKY_DIODE	0x4
>> >  
>> > +#define ABX8XX_REG_EXTRAM	0x3f
>> > +#define ABX8XX_EXTRAM_XADS	GENMASK(1, 0)
>> > +
>> > +#define ABX8XX_SRAM_BASE	0x40
>> > +#define ABX8XX_SRAM_WIN_SIZE	0x40
>> > +#define ABX8XX_RAM_SIZE		256
>> > +
>> > +#define NVMEM_ADDR_LOWER	GENMASK(5, 0)
>> > +#define NVMEM_ADDR_UPPER	GENMASK(7, 6)
>> > +
>> >  static u8 trickle_resistors[] = {0, 3, 6, 11};
>> >  
>> >  enum abx80x_chip {AB0801, AB0803, AB0804, AB0805,
>> > @@ -673,6 +684,68 @@ static int abx80x_setup_watchdog(struct abx80x_priv *priv)
>> >  }
>> >  #endif
>> >  
>> > +static int abx80x_nvmem_xfer(struct abx80x_priv *priv, unsigned int offset,
>> > +			     void *val, size_t bytes, bool write)
>> > +{
>> > +	int ret;
>> > +
>> > +	while (bytes) {
>> > +		u8 extram, reg, len, lower, upper;
>> > +
>> > +		lower = FIELD_GET(NVMEM_ADDR_LOWER, offset);
>> > +		upper = FIELD_GET(NVMEM_ADDR_UPPER, offset);
>> > +		extram = FIELD_PREP(ABX8XX_EXTRAM_XADS, upper);
>> > +		reg = ABX8XX_SRAM_BASE + lower;
>> > +		len = min(lower + bytes, (size_t)ABX8XX_SRAM_WIN_SIZE) - lower;
>> > +		len = min_t(u8, len, I2C_SMBUS_BLOCK_MAX);
>> > +
>> > +		ret = i2c_smbus_write_byte_data(priv->client, ABX8XX_REG_EXTRAM,
>> > +						extram);
>> > +		if (ret)
>> > +			return ret;
>> > +
>> > +		if (write)
>> > +			ret = i2c_smbus_write_i2c_block_data(priv->client, reg,
>> > +							     len, val);
>> > +		else
>> > +			ret = i2c_smbus_read_i2c_block_data(priv->client, reg,
>> > +							    len, val);
>> > +		if (ret)
>> > +			return ret;
>> > +
>> > +		offset += len;
>> > +		val += len;
>> > +		bytes -= len;
>> > +	}
>> > +
>> > +	return 0;
>> > +}
>> > +
>> > +static int abx80x_nvmem_read(void *priv, unsigned int offset, void *val,
>> > +			     size_t bytes)
>> > +{
>> > +	return abx80x_nvmem_xfer(priv, offset, val, bytes, false);
>> > +}
>> > +
>> > +static int abx80x_nvmem_write(void *priv, unsigned int offset, void *val,
>> > +			      size_t bytes)
>> > +{
>> > +	return abx80x_nvmem_xfer(priv, offset, val, bytes, true);
>> > +}
>> > +
>> > +static int abx80x_setup_nvmem(struct abx80x_priv *priv)
>> > +{
>> > +	struct nvmem_config config = {
>> > +		.type = NVMEM_TYPE_BATTERY_BACKED,
>> > +		.reg_read = abx80x_nvmem_read,
>> > +		.reg_write = abx80x_nvmem_write,
>> > +		.size = ABX8XX_RAM_SIZE,
>> > +		.priv = priv,
>> > +	};
>> > +
>> > +	return devm_rtc_nvmem_register(priv->rtc, &config);
>> > +}
>> > +
>> >  static int abx80x_probe(struct i2c_client *client,
>> >  			const struct i2c_device_id *id)
>> >  {
>> > @@ -824,6 +897,10 @@ static int abx80x_probe(struct i2c_client *client,
>> >  			return err;
>> >  	}
>> >  
>> > +	err = abx80x_setup_nvmem(priv);
>> > +	if (err)
>> > +		return err;
>> > +
>> >  	if (client->irq > 0) {
>> >  		dev_info(&client->dev, "IRQ %d supplied\n", client->irq);
>> >  		err = devm_request_threaded_irq(&client->dev, client->irq, NULL,
>> 
>> ping?
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/rtc/rtc-abx80x.c?id=e90ff8ede777b98b44611b416b1ae6be94258335
> 

Ah, thanks. I never heard anything about this so I assumed it got forgotten.

--Sean