Re: [PATCH v2 1/3] spi: tegra210-quad: Convert to hard IRQ with high-priority workqueue

[Breno Leitao <leitao@debian.org>]

Hello Vishwaroop,

On Wed, May 20, 2026 at 07:22:10PM +0000, Vishwaroop A wrote:
> On Wed, May 20, 2026 at 08:25:23AM -0700, Breno Leitao wrote:
> > > +     status = tegra_qspi_readl(tqspi, QSPI_TRANS_STATUS);
> > > +     if (!(status & QSPI_RDY))
> > > +             return IRQ_NONE;
> > > +
> > > +     spin_lock(&tqspi->lock);
> >
> > Can you help me to understand what the tqspi->lock protects? I am still
> > a bit confused by this lock, but at the first glance, I am wondering if
> > you don't need to have the lock while reading the status.
> 
> The lock itself protects the software state that is shared between
> the ISR, the workqueue bottom-half, and the timeout handler running
> in the transfer thread.

Thanks for the reply!

I got the impression that tqspi->lock is also serializing hardware
accesses — the hard IRQ holds it across the readl(QSPI_FIFO_STATUS) and
across tegra_qspi_mask_clear_irq(), which does an RMW on QSPI_INTR_MASK
and a W1C on QSPI_TRANS_STATUS; the setup, start, error and bottom-half
paths similarly hold it across MMIO.

If the lock is really only guarding curr_xfer / status_reg / tx_status
/ rx_status, why hold it across those register accesses at all?

Thanks,
--breno