On 3/11/22 9:25 PM, Simon Glass wrote:
Hi Sean,
On Thu, 3 Mar 2022 at 10:45, Sean Anderson sean.anderson@seco.com wrote:
Hi Simon,
On 3/1/22 9:58 AM, Simon Glass wrote:
Hi Sean,
On Mon, 28 Feb 2022 at 09:43, Sean Anderson sean.anderson@seco.com wrote:
On 2/26/22 1:36 PM, Simon Glass wrote:
Hi Sean,
On Mon, 7 Feb 2022 at 16:42, Sean Anderson sean.anderson@seco.com wrote:
This adds support for "nvmem cells" as seen in Linux. The nvmem device class in Linux is used for various assorted ROMs and EEPROMs. In this sense, it is similar to UCLASS_MISC, but also includes UCLASS_I2C_EEPROM, UCLASS_RTC, and UCLASS_MTD. While nvmem devices can be accessed directly, they are most often used by reading/writing contiguous values called "cells". Cells typically hold information like calibration, versions, or configuration (such as mac addresses).
nvmem devices can specify "cells" in their device tree:
qfprom: eeprom@700000 { #address-cells = <1>; #size-cells = <1>; reg = <0x00700000 0x100000>; /* ... */ tsens_calibration: calib@404 { reg = <0x404 0x10>; }; };which can then be referenced like:
tsens { /* ... */ nvmem-cells = <&tsens_calibration>; nvmem-cell-names = "calibration"; };The tsens driver could then read the calibration value like:
struct nvmem_cell cal_cell; u8 cal[16]; nvmem_cell_get_by_name(dev, "calibration", &cal_cell); nvmem_cell_read(&cal_cell, cal, sizeof(cal));Because nvmem devices are not all of the same uclass, supported uclasses must register a nvmem_interface struct. This allows CONFIG_NVMEM to be enabled without depending on specific uclasses. At the moment, nvmem_interface is very bare-bones, and assumes that no initialization is necessary. However, this could be amended in the future.
Although I2C_EEPROM and MISC are quite similar (and could likely be unified), they present different read/write function signatures. To abstract over this, NVMEM uses the same read/write signature as Linux. In particular, short read/writes are not allowed, which is allowed by MISC.
The functionality implemented by nvmem cells is very similar to that provided by i2c_eeprom_partition. "fixed-partition"s for eeproms does not seem to have made its way into Linux or into any device tree other than sandbox. It is possible that with the introduction of this API it would be possible to remove it.
Signed-off-by: Sean Anderson sean.anderson@seco.com
MAINTAINERS | 7 ++ doc/api/index.rst | 1 + doc/api/nvmem.rst | 7 ++ drivers/misc/Kconfig | 16 ++++ drivers/misc/Makefile | 1 + drivers/misc/nvmem.c | 109 +++++++++++++++++++++++++ include/nvmem.h | 185 ++++++++++++++++++++++++++++++++++++++++++ 7 files changed, 326 insertions(+) create mode 100644 doc/api/nvmem.rst create mode 100644 drivers/misc/nvmem.c create mode 100644 include/nvmem.h
Here I think it would be better to add a new uclass so that drivers which support it can add a child device in that uclass. This is done in lots of places in U-Boot.
I'm not sure exactly what you have in mind. The issue is that there are at least 6 uclasses which I would like to support:
- UCLASS_MISC
- UCLASS_I2C_EEPROM
- UCLASS_RTC
- UCLASS_MTD
- UCLASS_FUSE (doesn't exist yet, but probably should)
- Possibly UCLASS_PMIC
Most of these uclasses have existing interfaces which expose an NVMEM-like API, in addition to other uclass-specific functionality. Instead of having an additional API which drivers must implement, I would like to leverage these existing APIs to make adding NVMEM support as painless as possible. NVMEM is more of a "meta-uclass" which allows us to leverage existing read/write functions in uclasses. If any additional devices are to be created, they need to be created by the nvmem subsystem, or by the supported uclasses, rather than in drivers.
I may be missing something as I have not looked in detail at your API changes.
But the way to have a consistent API is to use a uclass. We do this with BLK. When a PMIC have GPIOs, RTC and regulators, we add them as child devices. We also have it with bootstd, where a bootdev is created as a child device of a storage device. We can put the required stuff in a helper function. We can even avoid any new code in the drivers by using the pending event system.
Can you first help me understand what is wrong with using a new uclass?
I suppose it could be done this way.
Effectively, we are "picking" out two functions from the existing API. NVMEM is a proper sub-uclass of every uclass added in this series except UCLASS_MISC (which just needs some API adjustment). In essence, we could actually implement something like nvmem_cell_read as
int nvmem_cell_read(struct nvmem_cell *cell, void *buf, size_t size) { dev_dbg(cell->nvmem, "%s: off=%u size=%zu\n", __func__, cell->offset, size); if (size != cell->size) return -EINVAL;
switch (cell->nvmem->driver->id) { case UCLASS_I2C_EEPROM: return i2c_eeprom_read(dev, offset, buf, size) case UCLASS_RTC: return dm_rtc_read(cell->nvmem, offset, buf, size); case UCLASS_MISC: { int ret = misc_read(cell->nvmem, offset, buf, size); if (ret < 0) return ret; if (ret != size) return -EIO; return 0; /* etc */ } } return -ENOSYS;}
Actually, that is probably cleaner than my current approach.
Yes but it is still not using a new uclass, right?
Right. But the idea is to use existing uclasses, because several of them effectively already implement the interface. See e.g. I2C and RTC which almost don't need a wrapper (except that they use different types for the size field).
--Sean