linux-kernel - Re: [PATCH v4 1/3] mtd: spi-nor: always use bounce buffer for register read/writes

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Message-ID: <2b10c18a-e955-31b8-b3e0-c3df83508756@ti.com>
Date:   Mon, 5 Aug 2019 16:08:57 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     <Tudor.Ambarus@...rochip.com>, <miquel.raynal@...tlin.com>,
        <richard@....at>
CC:     <marek.vasut@...il.com>, <bbrezillon@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
        <tmaimon77@...il.com>
Subject: Re: [PATCH v4 1/3] mtd: spi-nor: always use bounce buffer for
 register read/writes



On 05/08/19 2:36 PM, Tudor.Ambarus@...rochip.com wrote:
> 
> 
> On 08/01/2019 07:22 PM, Vignesh Raghavendra wrote:
>> External E-Mail
>>
>>
>> spi-mem layer expects all buffers passed to it to be DMA'able. But
>> spi-nor layer mostly allocates buffers on stack for reading/writing to
>> registers and therefore are not DMA'able. Introduce bounce buffer to be
>> used to read/write to registers. This ensures that buffer passed to
>> spi-mem layer during register read/writes is DMA'able. With this change
>> nor->cmd-buf is no longer used, so drop it.
>>
>> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
>> Signed-off-by: Vignesh Raghavendra <vigneshr@...com>
>> ---
>>
>> v4:
>> Avoid memcpy during READID
>>
>> v3: new patch
>>
>>  drivers/mtd/spi-nor/spi-nor.c | 70 ++++++++++++++++++++---------------
>>  include/linux/mtd/spi-nor.h   |  7 +++-
>>  2 files changed, 45 insertions(+), 32 deletions(-)
>>
>> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
>> index 03cc788511d5..e02376e1127b 100644
>> --- a/drivers/mtd/spi-nor/spi-nor.c
>> +++ b/drivers/mtd/spi-nor/spi-nor.c
> 
> cut
> 
>>  /**
>> @@ -1404,9 +1401,11 @@ static int write_sr_cr(struct spi_nor *nor, u8 *sr_cr)
>>  {
>>  	int ret;
>>  
>> +	memcpy(nor->bouncebuf, sr_cr, 2);
> 
> I'm thinking out loud. This can be avoided by forcing all the callers to use
> nor->bouncebuf. That would result in a:
> 

I can make this change and make all callers use nor->bouncebuf in next
version.

> static int write_sr(struct spi_nor *nor, size_t len)
> 
> write_sr_cr() can be removed. Memcopying 2 bytes is a small price to pay, we can
> keep things as they are, to not be too invasive. But if you think that this idea
> is worth it, tell.
> 

Sounds good to me. But replacing write_sr_cr() with above defintion of
write_sr() should be a patch IMO>

>> +
>>  	write_enable(nor);
>>  
>> -	ret = nor->write_reg(nor, SPINOR_OP_WRSR, sr_cr, 2);
>> +	ret = nor->write_reg(nor, SPINOR_OP_WRSR, nor->bouncebuf, 2);
>>  	if (ret < 0) {
>>  		dev_err(nor->dev,
>>  			"error while writing configuration register\n");
> 
> cut
> 
>> @@ -2177,9 +2176,10 @@ static const struct flash_info spi_nor_ids[] = {
>>  static const struct flash_info *spi_nor_read_id(struct spi_nor *nor)
>>  {
>>  	int			tmp;
>> -	u8			id[SPI_NOR_MAX_ID_LEN];
>> +	u8			*id;
>>  	const struct flash_info	*info;
>>  
>> +	id = nor->bouncebuf;
> 
> nit: do init at declaration.
> 

Ok.

> Also, you missed a place in which you can use the bouncebuf, search by "read_reg(":
> ret = nor->read_reg(nor, SPINOR_OP_XRDSR, &val, 1);
> 

Indeed, will fix in next version!

> Cheers,
> ta
> 

-- 
Regards
Vignesh