linux-kernel - Re: [PATCH v5 09/19] mtd: spi-nor: sfdp: parse xSPI Profile 1.0 table

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Message-ID: <20200521091434.rigqlyuwszyyikj4@ti.com>
Date:   Thu, 21 May 2020 14:44:36 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     <masonccyang@...c.com.tw>
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

On 21/05/20 04:09PM, masonccyang@...c.com.tw wrote:
> 
> Hi Pratyush, 
> 
> > > > > > +   /* 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.

As far as I know, the Profile 1.0 table only describes 8D-8D-8D mode. I 
see no mention of 8S-8S-8S in JESD251 or JESD216D.01. No field in the 
table describes anything related to 8S. In fact, searching for "8S" in 
the JESD251 spec yields 0 results. 

Anyway, you should set up 8S parameters in SNOR_CMD_READ_8_8_8, not 
SNOR_CMD_READ_8_8_8_DTR. 8D configuration is independent of 8S 
configuration.

PS: If you have any more comments, please send them now. The merge 
window is getting close, and I'd like to see this make it in.

-- 
Regards,
Pratyush Yadav
Texas Instruments India