linux-kernel - Re: [PATCH v2 4/4] spi: amd: Don't wait for a write-only transfer to finish

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Message-ID: <790250e3-a928-57d4-1378-bc8923163452@opensource.cirrus.com>
Date:   Fri, 10 Sep 2021 14:47:32 +0100
From:   Lucas tanure <tanureal@...nsource.cirrus.com>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>
CC:     Mark Brown <broonie@...nel.org>,
        Sanjay R Mehta <sanju.mehta@....com>,
        Nehal Bakulchandra Shah <Nehal-Bakulchandra.shah@....com>,
        <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH v2 4/4] spi: amd: Don't wait for a write-only transfer to
 finish

On 9/10/21 1:42 PM, Charles Keepax wrote:
> On Fri, Sep 10, 2021 at 12:15:29PM +0100, Lucas Tanure wrote:
>> Return from a write-only transfer without waiting for
>> it to finish
>> But wait before a new transfer as the previous may
>> still happening and also wait before reading the data
>> from the FIFO
>>
>> Signed-off-by: Lucas Tanure <tanureal@...nsource.cirrus.com>
>> ---
>> -static void amd_spi_execute_opcode(struct amd_spi *amd_spi)
>> +static int amd_spi_execute_opcode(struct amd_spi *amd_spi)
>>   {
>> +	int ret;
>> +
>> +	ret = amd_spi_busy_wait(amd_spi);
>> +	if (ret)
>> +		return ret;
>> +
>>   	/* Set ExecuteOpCode bit in the CTRL0 register */
>>   	amd_spi_setclear_reg32(amd_spi, AMD_SPI_CTRL0_REG, AMD_SPI_EXEC_CMD, AMD_SPI_EXEC_CMD);
>> -	amd_spi_busy_wait(amd_spi);
>> +
>> +	return 0;
>>   }
>>   
>>   static int amd_spi_master_setup(struct spi_device *spi)
>> @@ -178,6 +185,7 @@ static inline int amd_spi_fifo_xfer(struct amd_spi *amd_spi,
>>   			amd_spi_clear_fifo_ptr(amd_spi);
>>   			/* Execute command */
>>   			amd_spi_execute_opcode(amd_spi);
>> +			amd_spi_busy_wait(amd_spi);
> 
> Surely the previous transfer can't still be happening if this if
> unconditional? Should this not be gated on rx_len?
> 
> Thanks,
> Charles
> 
>>   			/* Read data from FIFO to receive buffer  */
>>   			for (i = 0; i < rx_len; i++)
>>   				buf[i] = amd_spi_readreg8(amd_spi, AMD_SPI_FIFO_BASE + tx_len + i);
>> -- 
>> 2.33.0
>>
This is executed inside an xfer->rx_buf not null if, so it`s gated in a 
read transfer and not for a write transfer only