Date:   Thu, 21 May 2020 16:09:52 +0800
From:   masonccyang@...c.com.tw
To:     "Pratyush Yadav" <p.yadav@...com>
Cc:     "Alexandre Belloni" <alexandre.belloni@...tlin.com>,
        "Boris Brezillon" <boris.brezillon@...labora.com>,
        "Mark Brown" <broonie@...nel.org>, juliensu@...c.com.tw,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-mtd@...ts.infradead.org,
        linux-spi@...r.kernel.org,
        "Ludovic Desroches" <ludovic.desroches@...rochip.com>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        "Miquel Raynal" <miquel.raynal@...tlin.com>,
        "Nicolas Ferre" <nicolas.ferre@...rochip.com>,
        "Sekhar Nori" <nsekhar@...com>,
        "Richard Weinberger" <richard@....at>,
        "Tudor Ambarus" <tudor.ambarus@...rochip.com>,
        "Vignesh Raghavendra" <vigneshr@...com>
Subject: Re: [PATCH v5 09/19] mtd: spi-nor: sfdp: parse xSPI Profile 1.0 table


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 
> 
> But the function that parses 4bait table is also called 
> spi_nor_parse_4bait(). 
> 
> > do others setting that has nothing to do with it, 
> 
> Why has setting read opcode and dummy cycles got nothing to do with it? 
> The purpose of the Profile 1.0 table is to tell us the Read Fast command 

> and dummy cycles, among other things. I think it _does_ have something 
> to do with it.

As you know I mean this function just do parse parameter of profile 1 
table
and keep these value data for later usage.

A device supports xSPI profile table could work in either 8S-8S-8S or 
8D-8D-8D mode.
It seems to setup these parameters somewhere out here is betters.

> 
> Just like the 4bait table tells us the 4-byte opcodes and we set them up 

> in our data structures, the profile 1.0 table tells us the 8D read 
> opcode and dummy cycles, and we set them up in our data structures.
> 
> > 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*
> 
> I mean from a design perspective. How does it make the code better, or 
> the job of people who need to read/change it easier?

yes, agreed.
I also need to patch for 8S-8S-8S mode, not only 8D-8D-8D mode.
That's why we have some discussions.

thanks & best regards,
Mason

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