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SubjectRe: [PATCH v5 09/19] mtd: spi-nor: sfdp: parse xSPI Profile 1.0 table
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Hi Pratyush,

> > > +/**
> > > + * spi_nor_parse_profile1() - parse the xSPI Profile 1.0 table
> > > + * @nor: pointer to a 'struct spi_nor'
> > > + * @param_header: pointer to the 'struct sfdp_parameter_header'
> > describing
> > > + * the 4-Byte Address Instruction Table length and version.
> > > + * @params: pointer to the 'struct spi_nor_flash_parameter' to
be.
> > > + *
> > > + * Return: 0 on success, -errno otherwise.
> > > + */
> > > +static int spi_nor_parse_profile1(struct spi_nor *nor,
> > > + const struct sfdp_parameter_header *profile1_header,
> > > + struct spi_nor_flash_parameter *params)
> > > +{
> > > + u32 *table, opcode, addr;
> > > + size_t len;
> > > + int ret, i;
> > > +
> > > + len = profile1_header->length * sizeof(*table);
> > > + table = kmalloc(len, GFP_KERNEL);
> > > + if (!table)
> > > + return -ENOMEM;
> > > +
> > > + addr = SFDP_PARAM_HEADER_PTP(profile1_header);
> > > + ret = spi_nor_read_sfdp(nor, addr, len, table);
> > > + if (ret)
> > > + goto out;
> > > +
> > > + /* Fix endianness of the table DWORDs. */
> > > + for (i = 0; i < profile1_header->length; i++)
> > > + table[i] = le32_to_cpu(table[i]);
> > > +
> > > + /* Get 8D-8D-8D fast read opcode and dummy cycles. */
> > > + opcode = FIELD_GET(PROFILE1_DWORD1_RD_FAST_CMD, table[0]);
> > > +
> > > + /*
> > > + * Update the fast read settings. We set the default dummy
cycles to
> > 20
> > > + * here. Flashes can change this value if they need to when
enabling
> > > + * octal mode.
> > > + */
> > > + spi_nor_set_read_settings(&params->reads[SNOR_CMD_READ_8_8_8_DTR],
> > > + 0, 20, opcode,
> > > + SNOR_PROTO_8_8_8_DTR);
> > > +
> >
> >
> > I thought we have a agreement that only do parse here, no other read
> > parameters setting.
>
> Yes, and I considered it. But it didn't make much sense to me to
> introduce an extra member in struct spi_nor just to make this call in
> some other function later.
>
> Why exactly do you think doing this here is bad? The way I see it, we
> avoid carrying around an extra member in spi_nor and this also allows
> flashes to change the read settings easily in a post-sfdp hook. The
> 4bait parsing function does something similar.

I think it's not a question for good or bad.

4bait parsing function parse the 4-Byte Address Instruction Table
and set up read/pp parameters there for sure.

Here we give the function name spi_nor_parse_profile1() but also
do others setting that has nothing to do with it,
it seems not good for SW module design.
oh, it's my humble opinion.


>
> What are the benefits of doing it otherwise?

For other Octal Flash like mx25*

>
> Note that I did remove HWCAPS selection from here, which did seem like a

> sane idea.
>
> > Driver should get dummy cycles used for various frequencies
> > from 4th and 5th DWORD of xSPI table.[1]
> >
> > [1]
> >
https://patchwork.ozlabs.org/project/linux-mtd/patch/1587451187-6889-3-git-

> send-email-masonccyang@mxic.com.tw/
> >
> >
> > In addition, 20 dummy cycles is for 200MHz but not for 100MHz, 133MHz
and
> > 166MHz
> > in case of read performance concern.
> >
> > Given a correct dummy cycles for a specific device. [2]
> >
> > [2]
> >
https://patchwork.ozlabs.org/project/linux-mtd/patch/1587451187-6889-5-git-

> send-email-masonccyang@mxic.com.tw/
>
> The problem is that we don't know what speed the controller is driving
> the flash at, and whether it is using Data Strobe. BFPT tells us the
> maximum speed of the flash based on if Data Strobe is being used. The
> controller can also drive it slower than the maximum. And it can drive
> it with or without DS.

This is for flash, not every Octal flash could work in 200MHz,
The Max operation speeds for other Octal Flash is 100, 133 , or 166MHz.

If a specific Octal Flash could work in 166MHz(Max), and driver setup the
correct 16 dummy cycles for it rather than 20 dummy cycles.
it's for performance concern.

>
> So, we have to be conservative and just use the dummy cycles for the
> maximum speed so we can at least make sure the flash works, albeit at
> slightly less efficiency. I hard-coded it to 20 but I suppose we can
> find it out from the Profile 1.0 table and use that (though we'd have to

> round it to an even value to avoid tripping up controllers). Will fix in

> next version (or, Tudor if you're fine with fixup! patches, I can send
> that too because I suspect it will be a small change).
>
> >

thanks & best regards,
Mason


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This e-mail and any attachments may contain confidential information and/or personal data, which is protected by applicable laws. Please be reminded that duplication, disclosure, distribution, or use of this e-mail (and/or its attachments) or any part thereof is prohibited. If you receive this e-mail in error, please notify us immediately and delete this mail as well as its attachment(s) from your system. In addition, please be informed that collection, processing, and/or use of personal data is prohibited unless expressly permitted by personal data protection laws. Thank you for your attention and cooperation.

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