Re: [PATCH v11 07/10] mtd: spi-nor: Add stacked memories support in spi-nor

[Tudor Ambarus <tudor.ambarus@linaro.org>]

On 12/8/23 17:06, Mahapatra, Amit Kumar wrote:
> Hello Tudor,

Hi!

> 
>> -----Original Message-----
>> From: Tudor Ambarus <tudor.ambarus@linaro.org>
>> Sent: Wednesday, December 6, 2023 8:14 PM
>> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra@amd.com>;
>> broonie@kernel.org; pratyush@kernel.org; miquel.raynal@bootlin.com;
>> richard@nod.at; vigneshr@ti.com; sbinding@opensource.cirrus.com;
>> lee@kernel.org; james.schulman@cirrus.com; david.rhodes@cirrus.com;
>> rf@opensource.cirrus.com; perex@perex.cz; tiwai@suse.com
>> Cc: linux-spi@vger.kernel.org; linux-kernel@vger.kernel.org;
>> michael@walle.cc; linux-mtd@lists.infradead.org;
>> nicolas.ferre@microchip.com; alexandre.belloni@bootlin.com;
>> claudiu.beznea@tuxon.dev; Simek, Michal <michal.simek@amd.com>; linux-
>> arm-kernel@lists.infradead.org; alsa-devel@alsa-project.org;
>> patches@opensource.cirrus.com; linux-sound@vger.kernel.org; git (AMD-
>> Xilinx) <git@amd.com>; amitrkcian2002@gmail.com
>> Subject: Re: [PATCH v11 07/10] mtd: spi-nor: Add stacked memories support
>> in spi-nor
>>
>>
>>
>> On 12/6/23 14:30, Tudor Ambarus wrote:
>>> Hi, Amit,
>>>
>>> On 11/25/23 09:21, Amit Kumar Mahapatra wrote:
>>>> Each flash that is connected in stacked mode should have a separate
>>>> parameter structure. So, the flash parameter member(*params) of the
>>>> spi_nor structure is changed to an array (*params[2]). The array is
>>>> used to store the parameters of each flash connected in stacked
>> configuration.
>>>>
>>>> The current implementation assumes that a maximum of two flashes are
>>>> connected in stacked mode and both the flashes are of same make but
>>>> can differ in sizes. So, except the sizes all other flash parameters
>>>> of both the flashes are identical.
>>>
>>> Do you plan to add support for different flashes in stacked mode? If
>>> not, wouldn't it be simpler to have just an array of flash sizes
>>> instead of duplicating the entire params struct?
>>>
>>>>
>>>> SPI-NOR is not aware of the chip_select values, for any incoming
>>>> request SPI-NOR will decide the flash index with the help of
>>>> individual flash size and the configuration type (single/stacked).
>>>> SPI-NOR will pass on the flash index information to the SPI core &
>>>> SPI driver by setting the appropriate bit in
>>>> nor->spimem->spi->cs_index_mask. For example, if nth bit of
>>>> nor->spimem->spi->cs_index_mask is set then the driver would
>>>> assert/de-assert spi->chip_slect[n].
>>>>
>>>> Signed-off-by: Amit Kumar Mahapatra <amit.kumar-
>> mahapatra@amd.com>
>>>> ---
>>>>  drivers/mtd/spi-nor/core.c  | 272 +++++++++++++++++++++++++++++-------
>>>>  drivers/mtd/spi-nor/core.h  |   4 +
>>>>  include/linux/mtd/spi-nor.h |  15 +-
>>>>  3 files changed, 240 insertions(+), 51 deletions(-)
>>>>
>>>> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
>>>> index 93ae69b7ff83..e990be7c7eb6 100644
>>>> --- a/drivers/mtd/spi-nor/core.c
>>>> +++ b/drivers/mtd/spi-nor/core.c
>>>
>>> cut
>>>
>>>> @@ -2905,7 +3007,10 @@ static void spi_nor_init_fixup_flags(struct
>>>> spi_nor *nor)  static int spi_nor_late_init_params(struct spi_nor
>>>> *nor)  {
>>>>  	struct spi_nor_flash_parameter *params = spi_nor_get_params(nor,
>> 0);
>>>> -	int ret;
>>>> +	struct device_node *np = spi_nor_get_flash_node(nor);
>>>> +	u64 flash_size[SNOR_FLASH_CNT_MAX];
>>>> +	u32 idx = 0;
>>>> +	int rc, ret;
>>>>
>>>>  	if (nor->manufacturer && nor->manufacturer->fixups &&
>>>>  	    nor->manufacturer->fixups->late_init) { @@ -2937,6 +3042,44 @@
>>>> static int spi_nor_late_init_params(struct spi_nor *nor)
>>>>  	if (params->n_banks > 1)
>>>>  		params->bank_size = div64_u64(params->size, params-
>>> n_banks);
>>>>
>>>> +	nor->num_flash = 0;
>>>> +
>>>> +	/*
>>>> +	 * The flashes that are connected in stacked mode should be of same
>> make.
>>>> +	 * Except the flash size all other properties are identical for all the
>>>> +	 * flashes connected in stacked mode.
>>>> +	 * The flashes that are connected in parallel mode should be identical.
>>>> +	 */
>>>> +	while (idx < SNOR_FLASH_CNT_MAX) {
>>>> +		rc = of_property_read_u64_index(np, "stacked-memories",
>> idx,
>>>> +&flash_size[idx]);
>>
>> also, it's not clear to me why you read this property multiple times.
>> Have you sent a device tree patch somewhere? It will help me understand
>> what you're trying to achieve.
> 
> Miquel submitted the device tree patch; here is the series.
> https://lore.kernel.org/all/20220126112608.955728-1-miquel.raynal@bootlin.com/
> 

oh, yes, I remember seeing this on the ml, but I couldn't allocate time
to review it. Looking at:
https://lore.kernel.org/all/20220126112608.955728-4-miquel.raynal@bootlin.com/

Flash size is not necessary for SPI NORs, as it can be discovered via
SFDP. And spi-max-frequency should have been specified for all flashes,
as I expect it can differ. At least so that the controller chooses the
minimum frequency from all the max (if it can't operate the stacks at
different frequencies).

Cheers,
ta