Messages in this thread | | | Date | Wed, 18 May 2022 10:51:58 +0200 | Subject | Re: [RFC PATCH 3/6] mtd: spi-nor: core: run calibration when initialization is done | From | Cédric Le Goater <> |
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Hello,
On 5/18/22 09:56, Pratyush Yadav wrote: > On 18/05/22 09:19AM, Miquel Raynal wrote: >> Hi Pratyush, >> >> p.yadav@ti.com wrote on Wed, 18 May 2022 11:37:05 +0530: >> >>> +Cedric >>> >>> On 17/05/22 04:02PM, Miquel Raynal wrote: >>>> Hi Pratyush, >>>> >>>> p.yadav@ti.com wrote on Fri, 12 Mar 2021 00:42:13 +0530: >>>> >>>>> Once the flash is initialized tell the controller it can run >>>>> calibration procedures if needed. This can be useful when calibration is >>>>> needed to run at higher clock speeds. >>>>> >>>>> Signed-off-by: Pratyush Yadav <p.yadav@ti.com> >>>>> --- >>>>> drivers/mtd/spi-nor/core.c | 12 ++++++++++-- >>>>> 1 file changed, 10 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c >>>>> index 88888df009f0..e0cbcaf1be89 100644 >>>>> --- a/drivers/mtd/spi-nor/core.c >>>>> +++ b/drivers/mtd/spi-nor/core.c >>>>> @@ -3650,6 +3650,7 @@ static int spi_nor_probe(struct spi_mem *spimem) >>>>> * checking what's really supported using spi_mem_supports_op(). >>>>> */ >>>>> const struct spi_nor_hwcaps hwcaps = { .mask = SNOR_HWCAPS_ALL }; >>>>> + struct spi_mem_op op; >>>>> char *flash_name; >>>>> int ret; >>>>> >>>>> @@ -3709,8 +3710,15 @@ static int spi_nor_probe(struct spi_mem *spimem) >>>>> if (ret) >>>>> return ret; >>>>> >>>>> - return mtd_device_register(&nor->mtd, data ? data->parts : NULL, >>>>> - data ? data->nr_parts : 0); >>>>> + ret = mtd_device_register(&nor->mtd, data ? data->parts : NULL, >>>>> + data ? data->nr_parts : 0); >>>>> + if (ret) >>>>> + return ret; >>>>> + >>>>> + op = spi_nor_spimem_get_read_op(nor); >>>> >>>> Isn't this too specific? I really don't know much about spi-nors, but I >>>> find odd to have this op being created here, why not moving this into >>>> the _do_calibration() helper? >>> >>> Maybe the naming confused you but this is a function in the SPI NOR >>> core, not in SPI MEM. SPI NOR supports both SPI MEM based controllers >>> and "legacy" controllers, so the convention is to add the "spimem" >>> prefix before SPI MEM specific functions. So I don't get the comment >>> about it being too specific. It is too specific to what? >> >> Mmh right, it's fine then. >> >>> >>> And how can spi_mem_do_calibration() know what op the flash uses to read >>> data? SPI NOR or SPI NAND would know it, but not SPI MEM. That is why we >>> pass in that information to spi_mem_do_calibration(). >> >> But here the op is "spi-nor wide", I would have expected a >> per-device op. But that is not a big deal, that is something that can >> also be updated later if needed I guess. > > It is per-device. The op is generated using nor->read_opcode, > nor->addr_width, nor->read_dummy, etc. So if you have 2 NOR flashes on > your system with different opcodes, it would work for both. > >> >> One last question, is there something that mtd_device_register() does >> that is really needed for the calibration to work? Otherwise I would >> rather prefer to have that calibration happening before the user gets >> access to the device.
Which would mean calling it right after :
ret = spi_nor_create_read_dirmap(nor); if (ret) return ret;
ret = spi_nor_create_write_dirmap(nor); if (ret) return ret;
> The calibration works by reading a known pattern that is already written > to the flash again and again and seeing what delays work and what don't. > For that to happen, the controller driver needs to know where the > pattern is stored.
Why don't you simply choose some random place, first 16KB for instance, and check that the data is random enough ? If not, declare calibration not possible and choose a default safe setting which is anyhow a requirement for calibration. Retry at reboot as data might have changed.
> This series does that by looking at the MTD > partitions. For that to happen, we need to create those partitions > first, which happens after mtd_device_register().
hmm, that might work for some boards. This is not at all the case for the BMC boards. Vendors can put any kind of flash model and/or layout and the driver needs to be more generic.
> But I am planning to use device tree to get that information now so this > should no longer be needed and we can do calibration before registering > the device with MTD.
Perfect, we can move the calibration hook in spi_nor_create_read_dirmap() then, or in devm_spi_mem_dirmap_create(), which would make more sense IMHO.
Thanks,
C.
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