Subject: Re: [PATCH 01/10] spi: dw: Add support for polled operation via no IRQ specified in DT

From: Lars Povlsen <[email-masked]>
Date: Tue, 9 Jun 2020 11:13:50 +0200

Serge Semin writes:

> On Wed, May 13, 2020 at 04:00:22PM +0200, Lars Povlsen wrote:
>> With this change a SPI controller can be added without having a IRQ
>> associated, and causing all transfers to be polled. For SPI controllers
>> without DMA, this can significantly improve performance by less
>> interrupt handling overhead.
>>
>> Reviewed-by: Alexandre Belloni <[email-masked]>
>> Signed-off-by: Lars Povlsen <[email-masked]>
>> ---
>>  drivers/spi/spi-dw.c | 21 +++++++++++++--------
>>  1 file changed, 13 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
>> index 31e3f866d11a7..e572eb34a3c1a 100644
>> --- a/drivers/spi/spi-dw.c
>> +++ b/drivers/spi/spi-dw.c
>> @@ -19,6 +19,8 @@
>>  #include <linux/debugfs.h>
>>  #endif
>>
>
>> +#define VALID_IRQ(i) (i >= 0)
>
> Mark and Andy are right. It is a good candidate to be in a generic IRQ-related
> code as Anyd suggested:
>
>> > drivers/rtc/rtc-cmos.c:95:#define is_valid_irq(n)               ((n) > 0)
>> > Candidate to be in include/linux/irq.h ?
>
> So if you feel like to author additional useful patch integrated into the
> kernel, this one is a good chance for it.
>

Yeah, but with the poll_transfer() gone below, I think I'll settle on
just getting this into the current framework. Optimization (as this is)
has less priority. I'll put this on the back burner.

>> +
>>  /* Slave spi_dev related */
>>  struct chip_data {
>>       u8 tmode;               /* TR/TO/RO/EEPROM */
>> @@ -359,7 +361,7 @@ static int dw_spi_transfer_one(struct spi_controller *master,
>>                       spi_enable_chip(dws, 1);
>>                       return ret;
>>               }
>> -     } else if (!chip->poll_mode) {
>> +     } else if (!chip->poll_mode && VALID_IRQ(dws->irq)) {
>>               txlevel = min_t(u16, dws->fifo_len / 2, dws->len / dws->n_bytes);
>>               dw_writel(dws, DW_SPI_TXFLTR, txlevel);
>>
>> @@ -379,7 +381,7 @@ static int dw_spi_transfer_one(struct spi_controller *master,
>>                       return ret;
>>       }
>>
>> -     if (chip->poll_mode)
>> +     if (chip->poll_mode || !VALID_IRQ(dws->irq))
>>               return poll_transfer(dws);
>
> Please note. The chip->poll and the poll_transfer() methods've been discarded
> from the driver, since commit 1ceb09717e98 ("spi: dw: remove cs_control and
> poll_mode members from chip_data"). So you gonna have to get the
> poll_transfer-like method back.
>
> -Sergey
>
>>
>>       return 1;
>> @@ -487,11 +489,13 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
>>
>>       spi_controller_set_devdata(master, dws);
>>
>> -     ret = request_irq(dws->irq, dw_spi_irq, IRQF_SHARED, dev_name(dev),
>> -                       master);
>> -     if (ret < 0) {
>> -             dev_err(dev, "can not get IRQ\n");
>> -             goto err_free_master;
>> +     if (VALID_IRQ(dws->irq)) {
>> +             ret = request_irq(dws->irq, dw_spi_irq, IRQF_SHARED,
>> +                               dev_name(dev), master);
>> +             if (ret < 0) {
>> +                     dev_err(dev, "can not get IRQ\n");
>> +                     goto err_free_master;
>> +             }
>>       }
>>
>>       master->use_gpio_descriptors = true;
>> @@ -539,7 +543,8 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
>>       if (dws->dma_ops && dws->dma_ops->dma_exit)
>>               dws->dma_ops->dma_exit(dws);
>>       spi_enable_chip(dws, 0);
>> -     free_irq(dws->irq, master);
>> +     if (VALID_IRQ(dws->irq))
>> +             free_irq(dws->irq, master);
>>  err_free_master:
>>       spi_controller_put(master);
>>       return ret;
>> --
>> 2.26.2
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> [email-masked]
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

-- 
Lars Povlsen,
Microchip

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