[PATCH v2 1/2] spi: call WATCHDOG_RESET() in spi_nor_wait_till_ready_with_timeout()

[Wolfgang Denk]

Dear Vignesh,

In message <05694b0e-50a1-de5d-25d8-0444a2caeff3 at ti.com> you wrote:
>
> Aim of spi-nor-tiny.c is to have a tiny stack that can be used in
> SPL/TPL or on resource constraint boards to only support _reading_ from
> the flash. So tiny stack would be subset of spi-nor-core.

I fully understand this goal.

> There are few options here:
> One is to have single driver and hide things that are not required for
> tiny stack under #ifdef. But this makes code harder to read and modify

#ifdef is one way to implement conditioan code, plain C code like

	if (IS_ENABLED(CONFIG_<something)) {
		...
	}

is another, usually much cleaner.

> Second option, is to factor out common functions into a separate file as
> a library. This would avoid ifdef'ry. But whenever a new feature is
> added that would add to the size of these common functions, it would be
> probably mean moving it out of common library and into individual
> stacks. This may need to unnecessary code churn whenever a new feature
> is added.

This is all speculation, and experience says that this risks and
disadvantages of duplicated code are much higher.

> So, suggestion was to add a parallel tiny stack (which was supposed to
> plug into tiny read only MTD stack) that only supports reading from
> flash. This would mean that new features can be freely added to
> spi-nor-core.c without worrying about bloating SPL for older devices.

Yes, and the result is that you have two different implementations
that are out of sync from day one after you created them, bugs get
fixed here but no there, support for new chips same, etc.

> If the opinion is to switch to second option now, then I can rework the
> framework. But note that this would make adding new features bit harder
> due to need to maintain size of spi-nor-tiny.c.

I agree that the reorganization will take additional efforts, but in
the long term, maintenance efforts will be much smaller, as you have
to maintain one common code base only.  And if you add new features
and see that they have negative impact on the SPL configurations,
you can always encapsulate these parts in IS_ENABLED() code.

> Please, let me know?

Well, for large parts things are pretty easy:

> > All the functions
> > 
> > 	spi_nor_read_write_reg()
> > 	spi_nor_read_reg()
> > 	spi_nor_write_reg()
> > 	spi_nor_read_data()
> > 	mtd_to_spi_nor()
> > 	spi_nor_convert_opcode()
> > 	spi_nor_ready()
> > 	spi_nor_wait_till_ready_with_timeout()
> > 	spi_nor_wait_till_ready()
> > 	macronix_quad_enable()
> > 	spansion_read_cr_quad_enable()
> > 	spi_nor_set_read_settings()
> > 
> > 
> > are absolutely identical;

For these functions there is absolutely no justification to have
them duplicated.

> > functions
> > 
> > 	read_cr()
> > 	write_sr()
> > 	write_disable()
> > 	set_4byte()
> > 	spi_nor_read()
> > 	write_sr_cr()
> > 
> > are mostly identical, but I wonder if the differences (like
> > nor->write_reg() versus spi_nor_write_reg()) is indeed intended to
> > save memory footprint or lack an update to later code?
>
> I am in the process of dropping nor->*() functions altogether as I don't
> see any users outside of spi-nor-core.c
>
> Note that some of these will no longer be same with 8D-8D-8D support[1]
> thus further reducing the similarities.

Well, maybe this rework should consider the idea of having common
code both for normal and size-limited use cases?

In the current form, the differences are so small they could easily
be handled by a few macro definitions so the code would be
indentical again.

Maybe this is also possible in your rework?

> > Function
> > 
> > 	spi_nor_convert_3to4_read()
> > 	spi_nor_set_4byte_opcodes()
> > 
> > looks like it has not been updated/synced for some time.
>
> Thats intentional... Adding Octal mode support to tiny stack would add
> to code size and possibly break few boards.

OK - I did not look deeply enough into the code if it was just new
features that will never be needed in the SPL, of if they might
actually be needed, or if they were actually bug fixes.

You are the expert here, so I trust your assessment.

> Any addition to spi-nor-tiny.c should be debated whether or not that
> change is absolutely needed for low footprint boards.

Agreed.

> > Function
> > 
> > 	spi_nor_sr_ready()
> > 	spi_nor_fsr_ready()
> > 
> > is lacking error handling in spi-nor-tiny.c; and the rror handling
> > code in spi-nor-core.c is also mostly duplicated a couple or times.
>
> Error handling is not required, as tiny stack does not support writing
> to flash and these errors are raised when writing or erasing flash.

These differences are tricial to handle using IS_ENABLED() for code
parts that are needed only when erase/write support is configured.


> > Function
> > 
> > 	spi_nor_read_id()
> > 
> > differs in "interesting" ways, i. e. we have 
> > 
> > 370         info = spi_nor_ids;
> > 371         for (; info->sector_size != 0; info++) {
> > 372                 if (info->id_len) {
> > 
> > here, and
>
> In case of tiny stack, we save space by not storing flash names in
> spi_nor_ids[] table (its a significant saving) and hence have to rely on
> another field to detect EOL.

You could still use the same method in both implementations, right?

> Duplication is to avoid feature creep leading to increase in code size.
> But I can factor out common code if there is a wider agreement.

Code duplication never evermakes sense to me. It is just a cause of
errors and mental pain.

I would really appreciate if youc ould clean this up.

Thanks!

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Veni, Vidi, VISA:
        I came, I saw, I did a little shopping.