linux-kernel - Re: [PATCH v2 09/28] spi: s3c64xx: use bitfield access macros

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Date: Fri, 26 Jan 2024 16:01:01 +0000
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Sam Protsenko <semen.protsenko@...aro.org>
Cc: broonie@...nel.org, andi.shyti@...nel.org, arnd@...db.de,
 robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
 alim.akhtar@...sung.com, linux-spi@...r.kernel.org,
 linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-arch@...r.kernel.org, andre.draszik@...aro.org,
 peter.griffin@...aro.org, kernel-team@...roid.com, willmcvicker@...gle.com
Subject: Re: [PATCH v2 09/28] spi: s3c64xx: use bitfield access macros

Hi, Sam,

I just noticed that I haven't responded to a question you had.

On 1/25/24 19:50, Sam Protsenko wrote:
> On Thu, Jan 25, 2024 at 8:50 AM Tudor Ambarus <tudor.ambarus@...aro.org> wrote:
>>
>> Use the bitfield access macros in order to clean and to make the driver
>> easier to read.
>>
>> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
>> ---
>>  drivers/spi/spi-s3c64xx.c | 196 +++++++++++++++++++-------------------
>>  1 file changed, 99 insertions(+), 97 deletions(-)
>>
>> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
>> index 1e44b24f6401..d046810da51f 100644
>> --- a/drivers/spi/spi-s3c64xx.c
>> +++ b/drivers/spi/spi-s3c64xx.c
>> @@ -4,6 +4,7 @@

cut

>> +#define S3C64XX_SPI_MAX_TRAILCNT_MASK          GENMASK(28, 19)

cut

>> +#define S3C64XX_SPI_CS_NSC_CNT_MASK            GENMASK(9, 4)

I was wrong introducing this mask because I can't tell if it applies to
all the versions of the IP. Thus I'll keep S3C64XX_SPI_CS_NSC_CNT_2
defined as (2 << 4) and add the following comment on top of it:

/*

 * S3C64XX_SPI_CS_NSC_CNT_2 is a value into the NCS_TIME_COUNT field. In
newer
 * datasheets this field is defined as GENMASK(9, 4). We don't know if
this mask
 * applies to all the versions of the IP, thus we can't yet define

 * S3C64XX_SPI_CS_NSC_CNT_2 as a value and the register field as a mask.

 */

#define S3C64XX_SPI_CS_NSC_CNT_2                (2 << 4)

cut

>> -#define S3C64XX_SPI_MAX_TRAILCNT       0x3ff
>> -#define S3C64XX_SPI_TRAILCNT_OFF       19
>> -
>> -#define S3C64XX_SPI_TRAILCNT           S3C64XX_SPI_MAX_TRAILCNT
>> -

cut

>> @@ -1091,8 +1094,7 @@ static void s3c64xx_spi_hwinit(struct s3c64xx_spi_driver_data *sdd)
>>
>>         val = readl(regs + S3C64XX_SPI_MODE_CFG);
>>         val &= ~S3C64XX_SPI_MODE_4BURST;
>> -       val &= ~(S3C64XX_SPI_MAX_TRAILCNT << S3C64XX_SPI_TRAILCNT_OFF);
> 
> Doesn't it change the behavior?

No, I don't think it does.

so above we wipe the mask, it's equivalent to:
val &= ~(GENMASK(28, 19))
> 
>> -       val |= (S3C64XX_SPI_TRAILCNT << S3C64XX_SPI_TRAILCNT_OFF);
and above we set the entire mask:
val |= GENMASK(28, 19)

the wipe is not necessary. This can be done in a separate patch of
course, but I considered that if I removed the shift, the value and
replaced them with the mask, I get the liberty of using the mask
directly. I'll split this op in a separate patch (it starts to feel tiring).

I verified the entire patch again, apart of the problem with the wrong
mask for S3C64XX_SPI_PSR_MASK and the problem that I specified with
S3C64XX_SPI_CS_NSC_CNT_MASK everything shall be fine. All the bits
handling shall be equivalent.