RE: [Patch V3 1/3] tpm_tis-spi: Support hardware wait polling

[Krishna Yarlagadda <kyarlagadda@xxxxxxxxxx>]

> -----Original Message-----
> From: Mark Brown <broonie@xxxxxxxxxx>
> Sent: 23 February 2023 22:49
> To: Krishna Yarlagadda <kyarlagadda@xxxxxxxxxx>
> Cc: robh+dt@xxxxxxxxxx; peterhuewe@xxxxxx; jgg@xxxxxxxx;
> jarkko@xxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx; linux-
> spi@xxxxxxxxxxxxxxx; linux-tegra@xxxxxxxxxxxxxxx; linux-
> integrity@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> thierry.reding@xxxxxxxxx; Jonathan Hunter <jonathanh@xxxxxxxxxx>;
> Sowjanya Komatineni <skomatineni@xxxxxxxxxx>; Laxman Dewangan
> <ldewangan@xxxxxxxxxx>
> Subject: Re: [Patch V3 1/3] tpm_tis-spi: Support hardware wait polling
> 
> On Thu, Feb 23, 2023 at 09:56:33PM +0530, Krishna Yarlagadda wrote:
> 
> > +       spi_bus_lock(phy->spi_device->master);
> > +
> > +       while (len) {
> 
> Why?
TPM supports max 64B in single transaction. Loop to send rest of it.
> 
> > +		spi_xfer[0].tx_buf = phy->iobuf;
> > +		spi_xfer[0].len = 1;
> > +		spi_message_add_tail(&spi_xfer[0], &m);
> > +
> > +		spi_xfer[1].tx_buf = phy->iobuf + 1;
> > +		spi_xfer[1].len = 3;
> > +		spi_message_add_tail(&spi_xfer[1], &m);
> 
> Why would we make these two separate transfers?
Tegra QSPI combined sequence requires cmd, addr and data in different
transfers. This eliminates need for additional flag for combined sequence.
> 
> > +		if (out) {
> > +			spi_xfer[2].tx_buf = &phy->iobuf[4];
> > +			spi_xfer[2].rx_buf = NULL;
> > +			memcpy(&phy->iobuf[4], out, transfer_len);
> > +			out += transfer_len;
> > +		}
> > +
> > +		if (in) {
> > +			spi_xfer[2].tx_buf = NULL;
> > +			spi_xfer[2].rx_buf = &phy->iobuf[4];
> > +		}
> 
> This will use the same buffer for rx and tx if some bug manages to leave
> them both set.  That shouldn't be an issue but it's an alarm bell
> reading the code.
> 
> > index 988aabc31871..b88494e31239 100644
> > --- a/include/linux/spi/spi.h
> > +++ b/include/linux/spi/spi.h
> > @@ -184,8 +184,9 @@ struct spi_device {
> >  	u8			chip_select;
> >  	u8			bits_per_word;
> >  	bool			rt;
> > -#define SPI_NO_TX	BIT(31)		/* No transmit wire */
> > -#define SPI_NO_RX	BIT(30)		/* No receive wire */
> > +#define SPI_NO_TX		BIT(31)		/* No transmit wire */
> > +#define SPI_NO_RX		BIT(30)		/* No receive wire */
> > +#define SPI_TPM_HW_FLOW		BIT(29)		/* TPM flow
> control */
> 
> Additions to the SPI API should be a separate commit for SPI rather than
> merged into a driver change.
Will split this into new patch.